feature: pmtiles verify

[bdon]

This should work against a local file only, verifying that:

• the clustered invariant holds
• tiles are contained within the file
• if gzipped, each referenced tile has the gzip magic bytes
• statistics are correct

Etc...

[bdon]

Implemented with checks for:

• metadata statistics
• clustered invariant
• tile bounds and min/maxzooms
• tile offset/length within correct range

More intense verify based on TileType can be added...