Replace deprecated GitHub Actions versions and update build
processes. Migrate from styfle/cancel-workflow-action to native
concurrency feature for canceling redundant builds. Update
checkout actions from v2/v3 to v4, setup-python from v2 to v5,
and cache from v3 to v4. Switch PyPI publishing to trusted
publishing with id-token and update build process from setup.py
to python -m build.

Add permissions sections to all workflows and fix macOS
environment variable handling by using GitHub ENV syntax instead
of shell exports. Remove legacy commented code and update cache
key generation.

Add comprehensive CONTRIBUTING.md with development environment
setup guide for both conda and manual setup, testing instructions,
and debugging guidance. Add .gitignore files to exclude generated
_version.py and notebook conversions.

Add two new steps to the CI workflow to cache pip packages between
runs. This reduces build time by reusing downloaded packages across
multiple CI jobs and re-runs.

The new steps retrieve the pip cache directory and use GitHub Actions
cache@v4 to store and restore it, keyed on the environment files and
setup.py to ensure cache validity.

The CI workflow now tests against Python versions 3.11, 3.12, 3.13,
and 3.14 explicitly. The setup-miniconda step now uses the
matrix-specified Python version, and cache keys for both conda and
pip environments are now versioned by Python version to prevent
cache conflicts.

Enable manual triggering of the CI workflow with customizable
parameters. Developers can now test specific Python versions
and operating systems without pushing code to the repository.

The workflow_dispatch event accepts two inputs: python-version
to test individual versions and os to select ubuntu-latest,
macos-latest, or all platforms. The matrix strategy was made
dynamic to respect these inputs.

Added documentation in CONTRIBUTING.md explaining how to
manually trigger workflows via GitHub Web Interface and CLI,
with practical use cases for testing specific configurations.

The main branch does not exist; this project uses the older
standard name, master.

Tighten scipy bound and add dependency update instructions

Update environment.yml to require scipy < 1.14 to avoid recent
compatibility breakages with velocileptors. Remove the obsolete
channel_priority line. Add a new "Updating dependencies" section to
CONTRIBUTING.md that documents how to update the conda environment,
reinstall pip-listed packages, and recreate the test environment for
contributors.

The separate isitgr and classy installation steps in the CI
workflow were redundant because both packages are already specified
in .github/environment.yml. More importantly, the isitgr step was
downgrading setuptools from 82.0.0 to <81 based on an outdated
workaround for setuptools issue #5174.

The local test environment successfully uses setuptools 82.0.0 with
isitgr 1.0.5 and classy 3.3.4.0, proving that the setuptools
downgrade is unnecessary. The CI now relies entirely on
environment.yml for package versions, matching the working local
configuration.

Consolidate developer documentation into readthedocs source files and
reference them from CONTRIBUTING.md to reduce duplication. Update
project requirements to Python 3.10+ and add missing build dependencies
to pyproject.toml.

Add a Makefile to streamline local package build testing and cleaning.
Update CI configuration to test Python 3.10. Standardize commands for
running tests and benchmarks with OMP_NUM_THREADS set to 2.

Update environment.yml with version constraints and comments.

Update build, CI and dependencies