fix: keep HybridOnlineStore routing_tag across FeatureViews

[jang-hs]

Fixes #6768

What this fixes

HybridOnlineStore.update() applies the first FeatureView and then fails on the second, no matter how the views are tagged:

ValueError: FeatureView must have a 'tribe' tag to use HybridOnlineStore.

The message reports 'tribe' even when the repo config sets a custom routing_tag, because that string is the fallback in

tag_name = getattr(config.online_store, "routing_tag", "tribe")

Getting the fallback means config.online_store is no longer the HybridOnlineStoreConfig by the time the second view is read. In practice this makes the store unusable for any repo with more than one FeatureView.

Root cause

1. _prepare_repo_conf mutated the caller's RepoConfig. rconfig = config is an alias, not a copy, so rconfig.online_config = ... and the data = rconfig.__dict__ writes all landed on the caller's object — replacing online_store with the selected backend's config. It also injected type into online_store.conf, which belongs to the user's config and is read again on the next lookup.

2. update() and teardown() rebound the config parameter inside their loops. Even with (1) fixed, the next iteration would receive the narrowed config instead of the hybrid one.

online_write_batch() and online_read() rebind as well, but those are single-use per call; fixing (1) is what makes them safe, so they are left as they are to keep the diff small.

The change

• _prepare_repo_conf builds its result from dict(config.__dict__) and constructs a new dict for the backend conf instead of injecting into the caller's. The returned kwargs are identical to what the mutating version produced — online_config and online_store are both set to the selected backend's conf, exactly as before — so nothing downstream changes.
• update() and teardown() assign the per-backend RepoConfig to a local store_config rather than rebinding config.

Tests

New unit test at sdk/python/tests/unit/infra/online_store/test_hybrid_online_store.py:

• test_update_routes_every_feature_view — two views with a custom routing_tag, one per backend; asserts both backends' update() are called once and the caller's routing_tag survives.
• test_prepare_repo_conf_does_not_mutate_caller_config — asserts the caller's online_store object and its conf dict are untouched.

Both fail on master and pass with this change:

# master
E   ValueError: FeatureView must have a 'tribe' tag to use HybridOnlineStore.
E   AssertionError: assert {'redis_type'...ype': 'redis'} == {'redis_type'...calhost:6379'}
2 failed

# with this change
2 passed

ruff check, ruff format --check, and mypy are clean on both files (the mypy errors that remain in the tree are pre-existing and in other modules).

The existing sdk/python/tests/integration/online_store/test_hybrid_online_store.py covers the write/read path; I could not run it locally as it needs testcontainers/Docker, but this change does not alter the config those paths receive.