[codex] Improve new user install and scheduling docs

[saulshanabrook]

Thank you @AYadrov and friends for the feedback! Still need to work on a larger docs refactor. Keep it coming!

Summary

This PR improves the first-run experience for new egglog-python users and fills in missing scheduling reference details.

• Add pip and uv install paths to the README and usage reference.
• Replace the conda-only getting-started notebook setup with pip and uv examples for Python 3.11+.
• Remove the stale conda-only docs/environment.yml file.
• Expand scheduling reference docs for run, saturate, * n, +, seq, and the backoff scheduler, including defaults, times_banned behavior, scheduler scoping, and :until limits.
• Add matching public docstrings for the Python schedule helpers.
• Update Cargo.lock's local package version to match Cargo.toml so source installs do not dirty the checkout.

Why

Users reported installation friction and undeclared-dependency symptoms. A fresh source install now resolves and runs through both pip and uv, and the docs no longer point new users at a conda-only environment path.

The scheduling docs also had the core examples, but did not comprehensively describe the Python schedule composition forms or backoff scheduler behavior.

Validation

• Fresh pip source install in .tmp/new-user-install-pip, then import/run smoke test.
• Fresh uv source install in .tmp/new-user-install-uv, then import/run smoke test.
• Imported egglog.examples.schedule_demo in both fresh environments.
• uv run pytest --benchmark-disable -q python/tests/test_high_level.py::TestScheduler python/tests/test_pretty.py (92 passed).
• make docs (succeeded; existing Sphinx/gallery warning noise remains).
• git diff --check.

[codspeed-hq]

Merging this PR will not alter performance

✅ 12 untouched benchmarks
⏩ 2 skipped benchmarks¹

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_{Comparing codex/new-user-usability-docs (295cfbd) with main (590864a)}

Footnotes

1. 2 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩