Add SCN specific startup for Oracle CDC

Oracle CDC lacked a first-class way to resume from a known Oracle SCN. The generic file/position specific-offset model did not match Oracle's redo-log offset shape, leaving users without a connector-owned SCN startup contract.

Added an Oracle-specific SCN option, mapped the configured SCN into the existing RedoLogOffset model, validated invalid combinations early, preserved checkpoint/restore behavior, and updated English and Chinese Oracle CDC docs.

• Enables Oracle CDC jobs to start incremental reading from an explicit valid SCN, a practical recovery and operations need for CDC pipelines.
• Keeps Oracle-specific startup semantics inside the Oracle connector while reusing SeaTunnel's shared StartupConfig.specificOffset(Map) and RedoLogOffsetFactory path.
• Fails fast for missing, non-positive, wrong-mode, or file/position combinations instead of silently falling back to another startup behavior.

• Added focused unit coverage for required SCN config, positive-SCN validation, RedoLogOffset mapping, split-state restore, wrong-mode rejection, and file/position rejection.
• Verified the Oracle CDC package from a clean reactor: 20 modules built successfully and all 15 Oracle tests passed.
• Ran Spotless checks and merged after maintainer approval confirmed the SCN startup contract was wired end to end with green CI.