Add initial Ramp Python SDK source

[zacatac]

Resolves EXT-1432

Summary

• publish the initial Ramp Python SDK source from core/pkgs/ramp_python
• add synchronous and asynchronous OAuth-authenticated clients and the generated Agent Tools surface
• add MIT licensing, public documentation, contribution and security guidance, packaging, and pinned GitHub Actions CI
• exclude Core-only generator inputs, overlays, specs, packaging metadata, private CI, and internal dependencies

Source commit: ramp/core@689e4f14d461d1bac63a90c06af07576d045563f
Source subtree: pkgs/ramp_python tree c68297395697e3c7884137b2027aa9461e90b893

Test plan

• uv run ruff format --check .
• uv run ruff check .
• uv run pytest -q — 23 passed
• Python 3.11 and 3.13 isolated test runs — 23 passed each
• ./scripts/verify_package.sh — sdist, wheel, license/typing inventory, and isolated Python 3.12 wheel smoke test
• staged-tree private-reference and credential scan

PyPI publication is intentionally deferred.