feat: Experiment cuts to dublets in seed finder (#2326)

This PR adds an option to include experimental specific cuts to discard bottom-middle dublets in a certain (r, eta) region of the detector.

This PR is related to the implementation of the ITk "fast tracking" configuration from PR #2166
(I am splitting the changes to make it more organised @CarloVarni @noemina)

For the integration with Athena we will need to implement something like that in Athena:
```
m_finderCfg.experimentCuts.connect(
	[](const void*, const float& bottomRadius, const float& cotTheta) -> bool {

        if (bottomRadius < fastTrackingRMin and
               (cotTheta > fastTrackingCotThetaMax or
                cotTheta < -fastTrackingCotThetaMax)) {
             return false;
        }
        return true;
}
```

where:

```
float fastTrackingRMin = 50. * Acts::UnitConstants::mm;
float fastTrackingCotThetaMax = 1.5;
```

Core/include/Acts/Seeding/SeedConfirmationRangeConfig.hpp

@@ -15,6 +15,11 @@
 
 namespace Acts {
 
+// defaults experimental cuts to no operation in both seeding algorithms
+inline bool noopExperimentCuts(float /*bottomRadius*/, float /*cotTheta*/) {
+  return true;
+}
+
 /// @brief contains parameters for  seed confirmation
 struct SeedConfirmationRangeConfig {
   // z minimum and maximum of middle component of the seed used to define the

Core/include/Acts/Seeding/SeedFinder.ipp

@@ -206,7 +206,11 @@ SeedFinder<external_spacepoint_t, platform_t>::getCompatibleDoublets(
     const float deltaRMinSP, const float deltaRMaxSP, const float uIP,
     const float uIP2, const float cosPhiM, const float sinPhiM) const {
   float impactMax = m_config.impactMax;
-  if constexpr (candidateType == Acts::SpacePointCandidateType::eBottom) {
+
+  constexpr bool isBottomCandidate =
+      candidateType == Acts::SpacePointCandidateType::eBottom;
+
+  if constexpr (isBottomCandidate) {
     impactMax = -impactMax;
   }
 
@@ -252,7 +256,7 @@ SeedFinder<external_spacepoint_t, platform_t>::getCompatibleDoublets(
     // the iterator so we don't need to look at the other SPs again
     for (; min_itr != otherSPs.end(); ++min_itr) {
       const auto& otherSP = *min_itr;
-      if constexpr (candidateType == Acts::SpacePointCandidateType::eBottom) {
+      if constexpr (isBottomCandidate) {
         // if r-distance is too big, try next SP in bin
         if ((rM - otherSP->radius()) <= deltaRMaxSP) {
           break;
@@ -272,7 +276,7 @@ SeedFinder<external_spacepoint_t, platform_t>::getCompatibleDoublets(
     for (; min_itr != otherSPs.end(); ++min_itr) {
       const auto& otherSP = *min_itr;
 
-      if constexpr (candidateType == Acts::SpacePointCandidateType::eBottom) {
+      if constexpr (isBottomCandidate) {
         deltaR = (rM - otherSP->radius());
 
         // if r-distance is too small, try next SP in bin
@@ -288,7 +292,7 @@ SeedFinder<external_spacepoint_t, platform_t>::getCompatibleDoublets(
         }
       }
 
-      if constexpr (candidateType == Acts::SpacePointCandidateType::eBottom) {
+      if constexpr (isBottomCandidate) {
         deltaZ = (zM - otherSP->z());
       } else {
         deltaZ = (otherSP->z() - zM);
@@ -379,6 +383,14 @@ SeedFinder<external_spacepoint_t, platform_t>::getCompatibleDoublets(
         const float iDeltaR = std::sqrt(iDeltaR2);
         const float cotTheta = deltaZ * iDeltaR;
 
+        // discard bottom-middle dublets in a certain (r, eta) region according
+        // to detector specific cuts
+        if constexpr (isBottomCandidate) {
+          if (!m_config.experimentCuts(otherSP->radius(), cotTheta)) {
+            continue;
+          }
+        }
+
         const float Er =
             ((varianceZM + otherSP->varianceZ()) +
              (cotTheta * cotTheta) * (varianceRM + otherSP->varianceR())) *
@@ -420,6 +432,14 @@ SeedFinder<external_spacepoint_t, platform_t>::getCompatibleDoublets(
       const float iDeltaR = std::sqrt(iDeltaR2);
       const float cotTheta = deltaZ * iDeltaR;
 
+      // discard bottom-middle dublets in a certain (r, eta) region according
+      // to detector specific cuts
+      if constexpr (isBottomCandidate) {
+        if (!m_config.experimentCuts(otherSP->radius(), cotTheta)) {
+          continue;
+        }
+      }
+
       const float Er =
           ((varianceZM + otherSP->varianceZ()) +
            (cotTheta * cotTheta) * (varianceRM + otherSP->varianceR())) *

Core/include/Acts/Seeding/SeedFinderConfig.hpp

@@ -173,6 +173,10 @@ struct SeedFinderConfig {
   // Returns position of the center of the top strip.
   Delegate<Acts::Vector3(const SpacePoint&)> getTopStripCenterPosition;
 
+  // Delegate to apply experiment specific cuts
+  Delegate<bool(float /*bottomRadius*/, float /*cotTheta*/)> experimentCuts{
+      DelegateFuncTag<&noopExperimentCuts>{}};
+
   bool isInInternalUnits = false;
 
   SeedFinderConfig toInternalUnits() const {

Core/include/Acts/Seeding/SeedFinderOrthogonal.ipp

@@ -226,6 +226,15 @@ bool SeedFinderOrthogonal<external_spacepoint_t>::validTuple(
     return false;
   }
 
+  /*
+   * Cut: Ensure that inner-middle dublet is in a certain (r, eta) region of the
+   * detector according to detector specific cuts.
+   */
+  const float rInner = (isMiddleInverted) ? rH : rL;
+  if (!m_config.experimentCuts(rInner, cotTheta)) {
+    return false;
+  }
+
   return true;
 }
 

Core/include/Acts/Seeding/SeedFinderOrthogonalConfig.hpp

@@ -11,6 +11,7 @@
 #include "Acts/Definitions/Algebra.hpp"
 #include "Acts/Definitions/Units.hpp"
 #include "Acts/Seeding/SeedConfirmationRangeConfig.hpp"
+#include "Acts/Utilities/Delegate.hpp"
 
 #include <memory>
 
@@ -109,6 +110,10 @@ struct SeedFinderOrthogonalConfig {
   float highland = 0;
   float maxScatteringAngle2 = 0;
 
+  // Delegate to apply experiment specific cuts
+  Delegate<bool(float /*bottomRadius*/, float /*cotTheta*/)> experimentCuts{
+      DelegateFuncTag<&noopExperimentCuts>{}};
+
   bool isInInternalUnits = false;
 
   SeedFinderOrthogonalConfig calculateDerivedQuantities() const {