Promote mixed numeric timeseries arithmetic to float

[FLABDUL]

Summary

• promote mixed integer/float timeseries arithmetic to float when either operand is float
• cover scalar and timeseries operands on both configured market backends
• make pull-request CI deterministic by using the locked Ruff version and reserving the protected Pages environment for release deployments

Closes #11

Validation

• focused timeseries tests — 26 passed
• full test suite — 262 passed, 3 skipped
• Ruff check and format check
• targeted Pyrefly check — 0 errors

Shared CI repair

This PR contains the same CI prerequisite commit as #9 and #12: Ruff is read from uv.lock using the Node 24 action, and GitHub Pages deployment is split from the pull-request docs build. The shared commit only needs to land once; it can be dropped from later PRs after the first is merged.