QASM conversion violates max_width in tk_SCRATCH_BIT register

[PabloAndresCQ]

According to the docstring of circuit_from_qasm, the user can set a "maximum allowed width of classical registers" with maxwidth. However, circuits that generate auxiliar tk_SCRATCH_BIT registers seem to skip this constraint.

Here is an example QASM file telep_Z_Z.txt. To reproduce, run:

from pytket.qasm import circuit_from_qasm
pytket_circuit = circuit_from_qasm("telep_Z_Z.txt", maxwidth=64)

The resulting pytket_circuit has a tk_SCRATCH_BIT register with more than 100 bits in it, violating the maxwidth=64 set by the user.

This is problematic in a pipeline where the pytket circuit is then converted to PHIR to be run in PECOS. For now, as a work around, I am using rename_units to convert each tk_SCRATCH_BIT[idx] to tk_SCRATCH_BIT_idx[0]. However, I would expect a better approach to create scratch registers of up to maxwidth size, and create new ones when the previous one is filled.