[python] Centralize PyPaimon packaging configuration

[Zouxxyy]

Purpose

Centralize PyPaimon's core, optional, development, and build dependencies in pyproject.toml, removing the two requirements files and duplicate CI dependency lists. Development groups reuse the public extras.

Use python -m build and generate the source distribution and wheel with the same date-stamped development version. Preserve commit provenance across source-distribution rebuilds and retain Python 3.6 compatibility. Update release workflows, installation docs, and lint exclusions for generated files.

Remove the obsolete packaging<26 cap so current Twine and PyPaimon can coexist in the same environment.

Tests

• Packaging integration tests: 7 passed on Python 3.6 and 7 passed on Python 3.11.
• Python 3.6 core tests: 115 passed, 7 skipped.
• Python 3.11 build-info, filesystem, schema, HDF5, and SQL tests: 77 passed, 1 skipped, including packaging 26.3.
• Verified editable dev installation with Twine 7, legacy group installation, isolated sdist installation, installed-wheel read/write, and pip check.
• Twine checks, Python lint and license headers, workflow YAML/shell syntax, root Spotless formatting, and git diff --check passed.

Full CI and mixed Java/Python E2E will run on GitHub.