Feature request: A5 cell support as object/search type

Problem

Tile38 supports Geohash, QuadKey, and XYZ tiles as cell-based object and search types, but no modern DGGS. A5 is a pentagonal DGGS (comparable to S2/H3) with equal-area cells at every resolution, low distortion, and cell IDs encoded as a 64-bit integer — a good fit alongside the existing tile/hash types. Related: #780 asks about H3 support; A5 has the practical advantage of a native Go implementation (no CGO), unlike H3's C bindings. GitHubA5geo

Proposal

Support A5 cells wherever Geohash/QuadKey work today: SET fleet truck1 A5 3778472949142978560 # set object as an A5 cell WITHIN fleet A5 3778472949142978560 # search by cell area INTERSECTS fleet A5 3778472949142978560 NEARBY ... / FENCE ... # fences over cell areas Internally a cell resolves to its pentagon boundary (polygon), so it can reuse the existing geometry path — same way QuadKey/tile areas are handled.

Implementation note

Native Go port exists: github.com/akhenakh/a5-go (no CGO). Reference implementations in TS/Python/Rust at a5geo.org for cross-validation.