feat: simplify chains of casts to be all in terms of the original `Va…

…lueId` (#3984)

…

# Description

## Problem\*

Resolves <!-- Link to GitHub Issue -->

## Summary\*

After #3946, `Instruction::Cast` is idempotent so we can replace the
`ValueId` being casted with the input to previous casts.

## Additional Context



## Documentation\*

Check one:
- [ ] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[Exceptional Case]** Documentation to be submitted in a separate
PR.

# PR Checklist\*

- [ ] I have tested the changes locally.
- [ ] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

Co-authored-by: kevaundray <kevtheappdev@gmail.com>

compiler/noirc_evaluator/src/ssa/ir/instruction.rs

@@ -546,6 +546,14 @@ impl Instruction {
 /// that value is returned. Otherwise None is returned.
 fn simplify_cast(value: ValueId, dst_typ: &Type, dfg: &mut DataFlowGraph) -> SimplifyResult {
     use SimplifyResult::*;
+    let value = dfg.resolve(value);
+
+    if let Value::Instruction { instruction, .. } = &dfg[value] {
+        if let Instruction::Cast(original_value, _) = &dfg[*instruction] {
+            return SimplifiedToInstruction(Instruction::Cast(*original_value, dst_typ.clone()));
+        }
+    }
+
     if let Some(constant) = dfg.get_numeric_constant(value) {
         let src_typ = dfg.type_of_value(value);
         match (src_typ, dst_typ) {