Fix asset watcher triggers deleted on every dag-parsing loop

[vatsrahul1001]

Summary

Fix asset watcher triggers being deleted and recreated on every dag-parsing loop.
encode_trigger wraps kwargs with BaseSerialization.serialize() (e.g., tuple() becomes
{"__type": "tuple", "__var": []}), which is correct for JSON-serializable DAG definitions.
However, add_asset_trigger_references needs raw Python kwargs because Trigger._decrypt_kwargs
returns native Python objects from the DB. This mismatch caused BaseEventTrigger.hash() to
produce different hashes for the same logical trigger, resulting in an infinite delete/recreate
cycle every parsing loop.
Replace encode_trigger with _get_raw_trigger_kwargs that unwraps any BaseSerialization-encoded
values back to native Python objects, ensuring hash consistency between DAG-defined and DB-stored
triggers. encode_trigger remains in use where it belongs — DAG serialization for JSON storage.

• Yes (please specify the tool below)
  Claude

• Read the Pull Request Guidelines for more information. Note: commit author/co-author name and email in commits become permanently public when merged.
• For fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
• When adding dependency, check compliance with the ASF 3rd Party License Policy.
• For significant user-facing changes create newsfragment: {pr_number}.significant.rst, in airflow-core/newsfragments. You can add this file in a follow-up commit after the PR is created so you know the PR number.

[TJaniF]

Tested with a local Kafka cluster and works great :)

[phanikumv]

Please add tests !

[kaxil]

Left few comments but lgtm directionally but will defer to @uranusjr and @Lee-W for 2nd pass