Support rewrite_manifests table maintenance

### Feature Request / Improvement

Rewriting manifests without changing data speeds up scan planning when a table has accumulated many small manifests. Java exposes this as `Table.rewriteManifests()` (Spark: `rewrite_manifests`).

Scope: an explicit maintenance operation that reads the current snapshot's manifests, regroups entries, rewrites them preserving sequence numbers (entries rewritten as EXISTING) and, for V3, `first_row_id`, and commits a `replace` snapshot. Related: #270 tracks automatic manifest merging on write; this covers the explicit maintenance API.

Locate the Python table maintenance/API entry point corresponding to Table.rewriteManifests(); read the current snapshot and manifest-management paths first. Done means an explicit operation regroups current manifests, preserves sequence numbers and V3 first_row_id, marks rewritten entries EXISTING, and commits a replace snapshot.

Written by the indexing model from the issue text.