feat(coverage): add Python 3.14 support and bump coverage.py to 7.10.7

[Syndic]

On rules_python 2.0.0, python.toolchain(configure_coverage_tool = True) is a silent no-op when python_version = "3.14": the bundled coverage.py wheel set in python/private/coverage_deps.bzl covers cp310–cp313 only, so bazel coverage produces zero-byte per-test lcov files for py_test targets. This PR bumps the bundled coverage to 7.10.7 (which ships cp39–cp314 wheels, including freethreaded variants for cp313+) and regenerates the wheel set.

• Regenerate coverage_deps.bzl against coverage 7.10.7
• Add cp314 (incl. freethreaded cp314t variants) to the bundled set
• Drop cp38 from the supported set (coverage.py 7.6.2 dropped Python 3.8)
• Extend update_coverage_deps.py's _supported_platforms map with the newer wheel platform tags (manylinux1_x86_64, macosx_10_13_x86_64) used by coverage 7.10.7
• Narrow coverage.patch context to apply against the 7.10.7 coverage/__main__.py layout
• Document the bundled coverage version range in docs/coverage.md

Verification:

• bazel test //tests/python:python_tests //tests/py_runtime:py_runtime_tests --test_tag_filters=-integration-test → 37/37 pass (incl. test_coverage_tool_executable, test_coverage_tool_plain_files)
• E2E: local_path_override this branch into a minimal external workspace, set python_version = "3.14" with configure_coverage_tool = True, run bazel coverage on a py_test → produces a non-empty per-test lcov with SF:, FNDA: reflecting actual call counts, and LH: non-zero

[gemini-code-assist]

Code Review

This pull request updates coverage.py to 7.10.7, adds support for Python 3.14 (including freethreaded variants), and drops support for Python 3.8. The changes span dependency definitions, documentation, and the dependency update tool. Feedback was provided regarding the placement of the CHANGELOG entry, suggesting it be moved to a more appropriate section.