feat: warn when running on an unsupported Python version

[not-matthias]

Print a warning in the pytest header when the running interpreter is outside the
Python version range pytest-codspeed claims to support:

WARNING: Python 3.16 is not officially supported by pytest-codspeed (supported:
3.9 to 3.15). Support is experimental and untested, measurements may be unreliable.

Customers upgrading Python currently get silent, unvalidated measurements: nothing
tells them the interpreter they benchmark on was never tested. Surfacing it in the
header means it lands in the CI log right under the existing codspeed: <version>
line, next to the other notices.

The bounds live in pytest_codspeed.utils and mirror requires-python plus the
Programming Language :: Python classifiers in pyproject.toml and the CI matrix.
The issue did not specify a list, and the sources disagreed: the classifiers and CI
say 3.15, while the README badge says 3.14 and the docs badge 3.13. The badges are
stale (docs still claimed 3.13 well after 3.14 classifiers shipped), so the bounds
follow the classifiers. Warning on 3.15 would contradict the package's own metadata
and redden the 3.15 CI legs.

test_get_python_version_warning_supported asserts no warning fires on the
interpreter running the suite, so adding a Python version to the CI matrix without
bumping the constant fails loudly instead of silently warning users.

Not included: the "warning on the Run page" half of the issue is platform-side. The
plugin already ships full interpreter metadata via get_environment_metadata and
collect_and_write_python_environment, so no extra plumbing is needed here.

Refs COD-3400

[codspeed-hq]

Merging this PR will degrade performance by 1.17%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 16 improved benchmarks
❌ 23 (👁 23) regressed benchmarks
✅ 238 untouched benchmarks

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Memory	test_multiprocessing_map[10]	4.1 MB	3.2 MB	+27.26%
⚡	WallTime	test_multiprocessing_map[1000]	59.2 ms	49.8 ms	+18.96%
⚡	WallTime	test_multiprocessing_map[100000]	419.4 ms	364.9 ms	+14.96%
⚡	WallTime	test_sum_of_squares[sum_of_squares_sum_labmda_power]	350.4 µs	312.5 µs	+12.13%
⚡	WallTime	test_multiprocessing_map[10000]	59.8 ms	56.2 ms	+6.36%
⚡	WallTime	test_sudoku[initial_grid0]	8.3 µs	7.9 µs	+4.97%
⚡	WallTime	test_open_knight_tour[1]	4.3 µs	4.1 µs	+4.66%
⚡	Memory	test_multiprocessing_map[100000]	6.2 MB	6 MB	+3.63%
⚡	WallTime	test_open_close_fd[10]	96.8 µs	93.4 µs	+3.61%
⚡	WallTime	test_make_lowpass	5.6 µs	5.5 µs	+2.75%
⚡	WallTime	test_make_peak	6.4 µs	6.3 µs	+2.7%
⚡	WallTime	test_hamilton_cycle[graph0]	25.5 µs	24.8 µs	+2.56%
⚡	WallTime	test_color[graph0-3]	31.4 µs	30.7 µs	+2.39%
⚡	WallTime	test_open_close_fd[100]	901.6 µs	880.6 µs	+2.37%
⚡	WallTime	test_recursive_fibo_20	5.3 ms	5.2 ms	+2.1%
⚡	WallTime	test_pipe_communication[100]	6.3 ms	6.2 ms	+2.09%
👁	WallTime	test_noop_pass_decorated	658.4 ns	804.6 ns	-18.16%
👁	WallTime	test_make_lowshelf	7.3 µs	7.7 µs	-5.18%
👁	WallTime	test_make_highpass	5.5 µs	5.7 µs	-3.82%
👁	WallTime	test_generate_sum_of_subsets_soln[nums0-9]	26.1 µs	29.3 µs	-10.98%
...	...	...	...	...	...

ℹ️ Only the first 20 benchmarks are displayed. Go to the app to view all benchmarks.

Tip

Curious why performance improved? Comment @codspeedbot explain why performance improved on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing cod-3400-warn-when-running-pytest-codspeed-with-unsupported-python (14b0bb9) with master (c7e9981)}

[not-matthias]

@greptileai review

[greptile-apps]

Greptile Summary

The PR adds a pytest-header notice when the active interpreter falls outside the supported Python 3.9–3.15 range.

• Defines supported-version bounds and formats local or GitHub Actions warnings.
• Adds unit and pytest integration coverage for supported, unsupported, and annotation output.

Confidence Score: 5/5

The PR appears safe to merge because no blocking failure remains.

No blocking failure remains.

Important Files Changed

Filename	Overview
src/pytest_codspeed/plugin.py	Adds supported-version bounds, warning formatting, and inclusion of the warning in pytest's report header.
tests/test_pytest_plugin.py	Adds tests for supported and unsupported versions, GitHub Actions annotations, and header integration.

_{Reviews (2): Last reviewed commit: "feat: warn when running on an unsupporte..." | Re-trigger Greptile}

[GuillaumeLagrange]

could use a hint of deslop for the tests, olgtm.

I wont highjack this one for the perf trampoline, let's merge this I'll make another PR