feat: add filter transformation for TimestampBasedKeyGenerator partition pruning

[yunchipang]

Description

Implements filter transformation for TimestampBasedKeyGenerator to enable partition pruning when user filters reference timestamp columns but partitions are organized by date components (year, month, day, hour).

• Add keygen module with KeyGeneratorFilterTransformer trait and TimestampBasedKeyGenerator
• Support all 6 timestamp types: UNIX_TIMESTAMP, EPOCHMILLISECONDS, EPOCHMICROSECONDS, DATE_STRING, SCALAR, MIXED
• Support input/output timezone configuration with proper fallback chain
• Support legacy hoodie.deltastreamer.keygen.timebased.* config prefix
• Support configurable scalar time units (NANOSECONDS through DAYS)
• Detect timestamp-based keygen via both hoodie.table.keygenerator.class (v6) and hoodie.table.keygenerator.type (v8+)
• Transform equality filters to multi-field partition filters (year, month, day, hour)
• Transform range filters (>, >=, <, <=) to inclusive bounds on the coarsest partition field
• Reject unsupported not-equal (!=) filters with a clear error message

Closes #286

How are the changes test-covered

• Automated tests (unit and/or integration tests)