feat: Announce geoparquet mirror size via STAC file extension

[A-Behairi]

Geoparquet collection mirrors now include their byte size, so the client can fetch the parquet footer without first probing for the file length. GitHub Pages compresses the file and a HEAD request does not return the actual file size, which points at the wrong offset.
This covers both catalogs generated with -gp, and collections pointing at an external ParquetSource. In the case of ParquetSource, the file could be republished without the collection reflecting its updated file:size , the client will have to expect the possibility of that and fallback accordingly.

[lubojr]

Thanks!
Good point with the ParquetSource catalog ref falling out of sync with the remote parquet file size, but as long as the client handling stays a possible optimization and not a mandatory property, that's fine!