Modernise profiler internals and CI

[joerick]

🤖 AI text below 🤖

• harden native profiler and sampler lifecycle error handling
• handle unset profiler context variables consistently
• preserve qualified class names in native frames
• improve asynchronous IPython compatibility and cleanup
• add Python 3.14 CI coverage and fix the wheel matrix
• replace Black and isort with Ruff, with a Nox lint session

Draft for CI validation.

AI assistance: Amp was used to help develop and test these changes.

[Copilot]

Pull request overview

This PR modernizes and hardens pyinstrument’s profiling internals (Python + native), expands test coverage around edge cases (contextvars, frame metadata, IPython async), and updates the project’s formatting/linting + CI matrices (including Python 3.14).

Changes:

• Harden stack sampler / native profiler lifecycle handling (rollback on failure, safer contextvar reads, tighter native error handling).
• Preserve qualified class names in native frame identifiers and add regression tests for “no locals” and nested classes.
• Modernize tooling/CI: move import sorting/formatting to Ruff + add Nox lint session + expand CI/test/wheel matrices (incl. 3.14 and ARM runners).

Reviewed changes

Copilot reviewed 23 out of 23 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/test_threading.py	Reorders imports to match new lint/format tooling.
test/test_stack_sampler.py	Adds regression test ensuring failed subscribe rolls back sampler state.
test/test_pstats_renderer.py	Reorders imports to match new lint/format tooling.
test/test_profiler.py	Adds session root-frame regression test and minor assertion formatting changes.
test/test_profiler_async.py	Reorders imports to match new lint/format tooling.
test/test_processors.py	Reorders imports to match new lint/format tooling.
test/test_ipython_magic.py	Adds async/IPython cleanup tests and warning filtering; imports asyncio.
test/test_context_manager.py	Reorders imports to match new lint/format tooling.
test/low_level/test_frame_info.py	Adds tests for nested qualified class names and frames with no locals.
test/low_level/test_custom_timer.py	Adds regression test ensuring invalid timer return values don’t leak references.
test/low_level/test_context.py	Adds coverage for contextvars without defaults in low-level profiler.
pyproject.toml	Introduces Ruff configuration (line length/target/excludes/import sorting).
pyinstrument/stack_sampler.py	Adds rollback logic in subscribe() to restore state on failures.
pyinstrument/session.py	Fixes trimming logic when start call stack is empty.
pyinstrument/magic/magic.py	Refactors run_cell_async to improve IPython async compatibility and cleanup.
pyinstrument/low_level/stat_profile.c	Improves contextvar handling, refcounting on errors, qualified class name extraction, and error paths.
pyinstrument/low_level/stat_profile_python.py	Aligns contextvar .get(None) behavior with native implementation.
pyinstrument/frame.py	Minor assertion formatting change.
noxfile.py	Adds a lint session using prek; expands test session to Python 3.14.
metrics/overhead.py	Formatting-only change (string quoting in f-string).
.pre-commit-config.yaml	Replaces isort/Black hooks with Ruff check + Ruff format.
.github/workflows/wheels.yml	Updates wheel build matrix to include ARM runner and removes QEMU setup.
.github/workflows/test.yml	Expands test matrix to Python 3.14 (incl. ARM).

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