Arbitrary qreg naming

[Asa-Kosto-QTM]

quantum registers can now be declared in multiple lines, for example:

qreg a[1]
qreg b[1]

instead of

qreg c[2]

[qartik]

Could you write a helper function to avoid duplication of these 4 lines of code in the two branches?

[qartik]

LGTM, left a comment for adding a helper function.

[qartik]

I have a few more suggestions after reading this part of the code:

@@ -24,7 +24,7 @@ def parse_shards_naive(
     shards_in_layer: list[ShardLayer] = []
     scheduled: set[int] = set()
     num_shards: int = len(shards)
-    qubit_id: int = 0
+    qid_count: int = 0
     qubits2ids: dict["UnitID", int] = {}
 
     while len(scheduled) < num_shards:
@@ -47,16 +47,12 @@ def parse_shards_naive(
             # map all the qubits to a unique id to prevent duplicates in placement
             if len(shard.qubits_used) != 2:  # noqa: PLR2004
                 for qubit in shard.qubits_used:
-                    qid, qubits2ids, qubit_id = assign_qubit_id(
-                        qubit, qubits2ids, qubit_id
-                    )
+                    qid, qid_count = get_qid(qubit, qubits2ids, qid_count)
                     op = [qid]
                     layer.append(op)
             else:
                 for qubit in shard.qubits_used:
-                    qid, qubits2ids, qubit_id = assign_qubit_id(
-                        qubit, qubits2ids, qubit_id
-                    )
+                    qid, qid_count = get_qid(qubit, qubits2ids, qid_count)
                     op.append(qid)
                 layer.append(op)
 
@@ -67,12 +63,11 @@ def parse_shards_naive(
     return layers, shards_in_layer
 
 
-def assign_qubit_id(
-    qubit: "UnitID", qubits2ids: dict["UnitID", int], qubit_id: int
-) -> tuple[int, dict["UnitID", int], int]:
-    """A helper function for managing qubit ids."""
-    if qubit not in qubits2ids:
-        qubits2ids[qubit] = qubit_id
-        qubit_id += 1
-    qid = qubits2ids[qubit]
-    return qid, qubits2ids, qubit_id
+def get_qid(
+    qubit: "UnitID", qubits2ids: dict["UnitID", int], qid_count: int
+) -> tuple[int, int]:
+    """Get qubit ID even if it is missing in the dict."""
+    qid = qubits2ids.setdefault(qubit, qid_count)
+    if qid == qid_count:
+        qid_count += 1
+    return qid, qid_count

If this looks okay @Asa-Kosto-QTM, I can push my commit here on this PR.

[Asa-Kosto-QTM]

@qartik looks smoother than the one I wrote. let's do it.