ci: check public API compatibility in pull requests

[shrishsk]

• This contribution adheres to CONTRIBUTING.md.
• I've updated CHANGELOG.md if applicable. No client-facing behavior changes.
• I've added tests applicable for this pull request. No permanent unit or system tests added for this CI configuration change; validated locally using temporary breaking-change probes.

What does this Pull Request accomplish?

Adds automated public API compatibility checks to the PR workflow using Griffe.

• Compares 29 API entry points against the PR's base commit, including all 25 modules referenced by the API documentation.
• Covers documented classes in private implementation modules, including collections and watchdog classes.
• Reports potential breaking changes through GitHub annotations and fails the job.
• Documents how contributors can reproduce compatibility checks locally.

The job uses read-only permissions, pinned actions, and Griffe 2.3.2. It requires no NI-DAQmx driver or package runtime dependencies.

Fixes #914.

Why should this Pull Request be merged?

Detects potential API-breaking changes before merging, rather than relying solely on internal tests after merge.

Checking documented implementation modules explicitly closes a verified coverage gap: checking nidaqmx.system alone did not detect removal of a documented collection property.

What testing has been done?

• Confirmed that all 25 documented modules are included in the 29-entry-point check.
• Ran the workflow's exact Bash command locally against unchanged APIs; it passed.
• Temporarily removed DeviceCollection.device_names; the expanded workflow command emitted a GitHub annotation and exited with code 1.
• poetry run ni-python-styleguide lint passed.
• poetry run mypy passed across 272 source files.
• npx cspell "**" --no-progress passed across 429 files.
• Workflow YAML and Bash syntax validation passed.
• Zizmor reported no medium-or-higher findings; an existing low-severity warning is unrelated to this change.

Temporary validation scripts, task configuration, and API modifications were removed. Hardware-dependent regression tests were not run.