feat(dbtype): time-based ID range queries for UUIDv7 and Int64

[klaidliadon]

Summary

• Add FloorUUIDv7 / CeilUUIDv7 / UUIDv7Time — synthetic UUIDv7 bounds and timestamp extraction using raw [16]byte, no external deps
• Add FloorInt64ID / CeilInt64ID / Int64IDTime — same for timestamp-embedded int64 IDs (typeid bit layout)
• Add TimeRange squirrel.Sqlizer that brackets a PK column with floor/ceil bounds derived from timestamps — enables WHERE id BETWEEN floor AND ceil queries using the PK index instead of a separate created_at column
• Convenience constructors: UUIDv7Range and Int64IDRange

Test plan

• 7 UUIDv7 tests: version/variant correctness, floor < real ordering, ceil > floor, bracket property, timestamp round-trip
• 5 Int64ID tests: floor/ceil ordering, bracket, timestamp round-trip, extraction
• 8 TimeRange tests: all four SQL output cases, accessor booleans, bound value correctness for both UUID and int64
• Existing bigint tests unaffected (24 total tests pass)