Test current Python versions in CI

[JarryShaw]

Summary

• add a weekly and pull-request compatibility matrix for CPython 3.10 through 3.14
• add Python 3.15 release-candidate coverage as a non-blocking preview lane
• run Conda maintenance on Python 3.14 and publish classifiers through Python 3.14

Local verification

• parsed all workflow YAML files
• parsed pyproject.toml
• imported PyPCAPKit with Python 3.14.7
• byte-compiled the package serially
• built the sdist and wheel in an isolated environment