fix: Unwrap SecretStr tokens when building Trino auth objects

[AdityaPatil22]

What this PR does / why we need it:

The Trino offline store fails when using JWT authentication: TypeError: can only concatenate str (not "SecretStr") to str
This happens because AuthConfig.to_trino_auth() passed model.model_dump() directly into Trino's auth classes. For JWT, the token field is a Pydantic SecretStr (to avoid leaking it in logs/reprs), but model_dump() leaves it as a SecretStr object instead of a plain string, and Trino's JWTAuthentication does "Bearer " + self.token internally, which fails on a non-str.

The fix unwraps any SecretStr fields via .get_secret_value() before constructing the Trino auth object, in to_trino_auth(). This is scoped to the auth boundary only — it doesn't touch _get_trino_client(), doesn't monkey-patch the Trino library, and doesn't change the user-facing config format. Other auth types (basic, kerberos, oauth2, certificate) are unaffected since none of their models use SecretStr.

Which issue(s) this PR fixes:

Fixes #6760

Checks

• I've made sure the tests are passing.
• My commits are signed off (git commit -s)
• My PR title follows conventional commits format

Testing Strategy

• Unit tests

Added sdk/python/tests/unit/infra/offline_stores/contrib/trino_offline_store/test_trino_auth.py:

• test_jwt_auth_produces_plain_str_token — verifies to_trino_auth() produces a JWTAuthentication whose .token is a plain str equal to the configured token, not a SecretStr.
• test_oauth2_auth_unchanged — verifies OAuth2 auth is unaffected by the change.

Ran the full trino_offline_store unit test suite (46 passed) plus ruff lint/format on modified files.

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 46.97%. Comparing base (03dac6f) to head (544d067).
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6771      +/-   ##
==========================================
+ Coverage   46.94%   46.97%   +0.02%     
==========================================
  Files         419      419              
  Lines       51839    51840       +1     
  Branches     7515     7515              
==========================================
+ Hits        24338    24350      +12     
+ Misses      25766    25755      -11     
  Partials     1735     1735              

Flag	Coverage Δ
go-feature-server	30.58% <ø> (ø)
python-unit	48.27% <100.00%> (+0.02%)	⬆️

Files with missing lines	Coverage Δ
...ffline_stores/contrib/trino_offline_store/trino.py	55.40% <100.00%> (+4.72%)	⬆️

... and 1 file with indirect coverage changes

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