feat: Expand SimpleReplacement API

[lmondada]

I would like to reuse the replacement logic in tket2, so I've taken the opportunity to expand the API of SimpleReplacement and refactor things a bit.

[codecov]

Codecov Report

Attention: Patch coverage is 80.98592% with 27 lines in your changes missing coverage. Please review.

Project coverage is 83.75%. Comparing base (242e12f) to head (6bddd76).

Files with missing lines	Patch %	Lines
hugr-core/src/hugr/rewrite/simple_replace.rs	81.25%	23 Missing and 1 partial ⚠️
hugr-core/src/hugr/rewrite/port_types.rs	78.57%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1920      +/-   ##
==========================================
- Coverage   83.78%   83.75%   -0.04%     
==========================================
  Files         196      197       +1     
  Lines       37470    37537      +67     
  Branches    34283    34350      +67     
==========================================
+ Hits        31396    31438      +42     
- Misses       4296     4320      +24     
- Partials     1778     1779       +1     

Flag	Coverage Δ
python	92.34% <ø> (ø)
rust	82.95% <80.98%> (-0.04%)	⬇️

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