feat: InlineFunctionsPass

[aborgna-q]

Adds a pass definition that calls the already-defined function inlining tool.

This version uses a simple heuristic to choose when to inline:

• Function must not be on a cycle of the call-graph (i.e. it's not recursive).
• The function definition must have a limited number of nodes (defaults to <= 64 descendants).

We can add better heuristicts in the future, and check for inline hints.
This is a first version to help with simple optimization cases.

Note that the inlined funcDefs are not removed. RemoveDeadFuncsPass can be called afterwards to remove what's not needed.

We should also add this as a first step in NormalizeGuppy

[codecov]

Codecov Report

❌ Patch coverage is 82.65306% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.80%. Comparing base (a7f40bb) to head (08019c6).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
tket/src/passes/inline_funcs.rs	78.26%	14 Missing and 1 partial ⚠️
tket-py/tket/passes/__init__.py	90.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1524      +/-   ##
==========================================
- Coverage   83.82%   83.80%   -0.03%     
==========================================
  Files         187      188       +1     
  Lines       28954    29032      +78     
  Branches    27875    27928      +53     
==========================================
+ Hits        24271    24330      +59     
- Misses       3522     3540      +18     
- Partials     1161     1162       +1     

Flag	Coverage Δ
python	92.32% <93.10%> (-0.01%)	⬇️
qis-compiler	91.66% <ø> (ø)
rust	83.46% <78.26%> (-0.03%)	⬇️

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[cqc-alec]

Thanks, just small comments.

[cqc-alec]

Maybe this should be called something like InlineSmallFunctionsPass, since the name suggests that it inlines all functions.

[aborgna-q]

I don't think we want to limit ourselves to only small functions here.

The max_size limit is the simplest of the heuristics we could apply.

We may want to add alternatives in the future that decide based on the function types or something else.

We'll also want to add the option to inline functions based on inline hints in their metadata.

I think I'll add an InlineHeuristic enum instead of the max_size flag.

Do you have an alternative name suggestion that also works for different heuristics?

[cqc-alec]

Sounds good to me. I think the name is fine if it is referring to a general heuristic.

[cqc-alec]

Maybe rename to inline_small_functions? Alternatively we could have max_inline_size be optional and if not set inline all functions?

[aborgna-q]

I'd like to have the default behaviour be useful. I don't think "inline everything" is something users will want to do most of the time.

See my comment about a Heuristics enum below. I'll add an All variant.

[aborgna-q]

Added the heuristic enum, and a flag for following inline hints.
(The inline hint metadata will come in a separate PR, but we can at least stabilize the pass API now).

I'm using Protocols for the python heuristics, since python enums can't carry data. Not sure if I love this design, but it works.

[cqc-alec]

LGTM