perf: coordinate reverse positions aggregation APIs

[samukweku]

Summary

Coordinate the pyjanitor calls for all five reverse positions aggregations. Remove the redundant length argument from the positions wrappers and dispatch only the remaining positions aggregations with that argument.

Related

• janitor-rs Convert malab date #100
• janitor-rs Implemented concatenate and deconcatenate columns #23
• Documentation issue docs: explain conditional_join and reverse-aggregation index representations #1688

Verification

• Pre-commit checks passed for formatting, lint, and docstring validation
• Python syntax checks passed
• Rust-side tests and old-vs-compact benchmarks are included in the five corresponding janitor-rs PRs

Runtime tests and benchmark execution remain pending because the local macOS host lacks the configured Python 3.9 framework.

[samukweku]

Contract documentation is now included in this PR and its branch AGENTS.md.

• Direct Rust reverse-match kernels reject an empty flattened matches tape; malformed tape shape is not silently accepted.
• A batch with no candidates at all is valid at the Python level, so pyjanitor pre-filters that case and returns the normal typed empty result before dispatching to Rust.
• Individual zero-width ranges remain valid when the overall tape is non-empty.
• The comparison/producer layer owns the matches values-in-{0,1} invariant; the Rust boundary validates tape shape.
• The compatibility length argument exists only for older janitor-rs wheels.

An ELI5 explanation is included in the Python module docstring and AGENTS.md.