feat: Add compiler warning framework with opt-in rich warning rendering

[ss2165]

Closes #1654

This adds the base compiler warning framework for guppylang. Warnings are now first-class non-fatal diagnostics that are buffered across a top-level check() or compile() operation, deduplicated within that operation, and emitted through Python’s warnings system as guppylang.GuppyWarning.

The change also adds an opt-in rich warning mode via with guppylang.rich_warnings(): .... In that mode, Guppy still emits the normal Python warning for filtering/tooling compatibility, and additionally renders the full warning diagnostic with source context to stderr.

What’s included:

• warning session plumbing in the diagnostics/error layer;
• public guppylang.GuppyWarning;
• public guppylang.rich_warnings() context manager;
• single-flush behaviour across nested compiler entrypoints and GuppyLibrary multi-call flows;
• framework, integration, renderer, and notebook coverage for the new warning surfaces.

Unreachable-code warning production in follow up: #1660

Developed iteratively with Codex, see individual commits for steps.

[github-actions]

Bencher Report

Branch	ss/push-kvqpqswszwxo
Testbed	Linux

Click to view all benchmark results

Benchmark	Latency	Benchmark Result microseconds (µs) (Result Δ%)	Upper Boundary microseconds (µs) (Limit %)
tests/benchmarks/test_big_array.py::test_big_array_check	📈 view plot 🚷 view threshold	662,369.80 µs (-26.13%) Baseline: 896,642.24 µs	941,474.36 µs (70.35%)
tests/benchmarks/test_big_array.py::test_big_array_compile	📈 view plot 🚷 view threshold	1,951,226.64 µs (-2.56%) Baseline: 2,002,456.76 µs	2,102,579.60 µs (92.80%)
tests/benchmarks/test_big_array.py::test_big_array_executable	📈 view plot 🚷 view threshold	8,611,560.05 µs (+1.40%) Baseline: 8,492,709.08 µs	8,917,344.53 µs (96.57%)
tests/benchmarks/test_ctrl_flow.py::test_many_ctrl_flow_check	📈 view plot 🚷 view threshold	98,985.74 µs (-7.37%) Baseline: 106,855.86 µs	112,198.66 µs (88.22%)
tests/benchmarks/test_ctrl_flow.py::test_many_ctrl_flow_compile	📈 view plot 🚷 view threshold	221,032.94 µs (-5.38%) Baseline: 233,604.41 µs	245,284.63 µs (90.11%)
tests/benchmarks/test_ctrl_flow.py::test_many_ctrl_flow_executable	📈 view plot 🚷 view threshold	964,152.76 µs (-24.02%) Baseline: 1,268,885.61 µs	1,332,329.89 µs (72.37%)
tests/benchmarks/test_prelude.py::test_import_guppy	📈 view plot 🚷 view threshold	44.42 µs (-13.93%) Baseline: 51.60 µs	54.18 µs (81.97%)
tests/benchmarks/test_queue_push_pop.py::test_queue_push_benchmark	📈 view plot 🚷 view threshold	480,429.96 µs (+1.55%) Baseline: 473,098.74 µs	496,753.68 µs (96.71%)
tests/benchmarks/test_queue_push_pop.py::test_queue_push_pop_benchmark	📈 view plot 🚷 view threshold	633,318.87 µs (+2.20%) Baseline: 619,709.84 µs	650,695.33 µs (97.33%)

🐰 View full continuous benchmarking report in Bencher

[github-actions]

Bencher Report

Branch	ss/push-kvqpqswszwxo
Testbed	Linux

Click to view all benchmark results

Benchmark	hugr_bytes	Benchmark Result bytes x 1e3 (Result Δ%)	Upper Boundary bytes x 1e3 (Limit %)	hugr_nodes	Benchmark Result nodes x 1e3 (Result Δ%)	Upper Boundary nodes x 1e3 (Limit %)
tests/benchmarks/test_big_array.py::test_big_array_compile	📈 view plot 🚷 view threshold	158.77 x 1e3 (0.00%) Baseline: 158.77 x 1e3	160.36 x 1e3 (99.01%)	📈 view plot 🚷 view threshold	6.64 x 1e3 (0.00%) Baseline: 6.64 x 1e3	6.71 x 1e3 (99.01%)
tests/benchmarks/test_ctrl_flow.py::test_many_ctrl_flow_compile	📈 view plot 🚷 view threshold	27.53 x 1e3 (0.00%) Baseline: 27.53 x 1e3	27.81 x 1e3 (99.01%)	📈 view plot 🚷 view threshold	1.07 x 1e3 (0.00%) Baseline: 1.07 x 1e3	1.08 x 1e3 (99.01%)

🐰 View full continuous benchmarking report in Bencher

[codecov-commenter]

Codecov Report

❌ Patch coverage is 92.56198% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.55%. Comparing base (8900c4c) to head (7dcbcc3).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ylang-internals/src/guppylang_internals/warning.py	94.39%	6 Missing ⚠️
guppylang/src/guppylang/defs.py	57.14%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1659      +/-   ##
==========================================
+ Coverage   93.54%   93.55%   +0.01%     
==========================================
  Files         133      134       +1     
  Lines       12640    12757     +117     
==========================================
+ Hits        11824    11935     +111     
- Misses        816      822       +6     

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[mark-koch]

Consider using the existing Span class instead

[mark-koch]

It would be very cool if we could use set[Warning] here, it already includes the span and the message

This would require hashability, but maybe we can just force the new Warning subclass to be hashable instead of all Diagnostics?