perf: Return Cow<Signature> where possible

[aborgna-q]

group                                    cows                                   serialization
-----                                    ----                                   -------------
circuit_roundtrip/capnp/0                1.02      5.3±0.52µs        ? ?/sec    1.00      5.2±0.09µs        ? ?/sec
circuit_roundtrip/capnp/1                1.00     12.5±0.74µs        ? ?/sec    1.14     14.2±0.16µs        ? ?/sec
circuit_roundtrip/capnp/10               1.00     25.9±0.39µs        ? ?/sec    1.31     34.0±0.30µs        ? ?/sec
circuit_roundtrip/capnp/100              1.00    155.8±2.01µs        ? ?/sec    1.47    229.6±2.46µs        ? ?/sec
circuit_roundtrip/capnp/1000             1.00  1483.7±64.06µs        ? ?/sec    1.43      2.1±0.04ms        ? ?/sec
circuit_roundtrip/capnp/10000            1.00     15.9±0.26ms        ? ?/sec    1.49     23.7±1.67ms        ? ?/sec
circuit_roundtrip/capnp/100000           1.00    192.8±2.26ms        ? ?/sec    1.37    264.3±5.44ms        ? ?/sec
circuit_roundtrip/capnp/200000           1.00    411.5±4.77ms        ? ?/sec    1.36   560.4±15.52ms        ? ?/sec
circuit_roundtrip/capnp/300000           1.00    648.9±5.40ms        ? ?/sec    1.34   871.5±10.63ms        ? ?/sec
circuit_roundtrip/json/0                 1.00      8.0±0.18µs        ? ?/sec    1.00      8.0±0.14µs        ? ?/sec
circuit_roundtrip/json/1                 1.00     19.0±0.27µs        ? ?/sec    1.16     22.1±0.33µs        ? ?/sec
circuit_roundtrip/json/10                1.00     50.0±0.68µs        ? ?/sec    1.26     63.0±0.94µs        ? ?/sec
circuit_roundtrip/json/100               1.00    342.5±4.81µs        ? ?/sec    1.30    446.4±4.61µs        ? ?/sec
circuit_roundtrip/json/1000              1.00      3.4±0.03ms        ? ?/sec    1.31      4.5±0.35ms        ? ?/sec
circuit_roundtrip/json/10000             1.00     37.2±0.73ms        ? ?/sec    1.28     47.5±0.45ms        ? ?/sec
circuit_roundtrip/json/100000            1.00    399.3±8.46ms        ? ?/sec    1.27   507.7±16.13ms        ? ?/sec
circuit_roundtrip/json/1000000           1.00       4.5±0.26s        ? ?/sec    1.20       5.4±0.06s        ? ?/sec

Closes #1741

[codecov]

Codecov Report

Attention: Patch coverage is 93.54839% with 8 lines in your changes missing coverage. Please review.

Project coverage is 86.28%. Comparing base (f2215e9) to head (a9732c6).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
hugr-core/src/ops/constant.rs	40.00%	3 Missing ⚠️
hugr-core/src/extension/resolution/ops.rs	0.00%	2 Missing ⚠️
hugr-core/src/hugr/rewrite/replace.rs	0.00%	2 Missing ⚠️
hugr-core/src/package.rs	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1743      +/-   ##
==========================================
+ Coverage   86.27%   86.28%   +0.01%     
==========================================
  Files         179      179              
  Lines       32476    32513      +37     
  Branches    29388    29425      +37     
==========================================
+ Hits        28018    28054      +36     
- Misses       2758     2759       +1     
  Partials     1700     1700              

Flag	Coverage Δ
python	92.42% <ø> (ø)
rust	85.64% <93.54%> (+0.01%)	⬆️

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[acl-cqc]

Big +1 to this, although I have not looked in detail.

Should we consider returning a Signature struct that contains Cow<TypeRow>, Cow<TypeRow>, Cow<ExtensionSet>....?

[aborgna-q]

There's another discussion on what to do about type_rows, but yes we should do some sharing at some point.

This was just a really low hanging fruit for optimisation.

[aborgna-q]

I had to add a small workaround for #1758, since now we actually check the extension_reqs that come from the serialized hugr.

I'll fix it in another PR