Support user-provided schema for Parquet reads

[sfc-gh-dyadav]

Allow users to specify a custom schema when reading Parquet files via session.read.schema(schema).parquet(path). Previously only JSON and XML supported user-provided schemas; Parquet was blocked by a ValueError gate.

• Add "parquet" to the user-schema format allowlist in _read_semi_structured_file
• Update schema() docstring to reflect all supported formats
• Remove stale ValueError assertion in test_read_parquet_with_no_schema
• Add test_read_parquet_user_input_schema covering matching schema, missing columns, extra columns, and wrong-type error cases

Made-with: Cursor

1. Which Jira issue is this PR addressing? Make sure that there is an accompanying issue to your PR.

   Fixes SNOW-3242298

2. Fill out the following pre-review checklist:

   • I am adding a new automated test(s) to verify correctness of my new code
     • If this test skips Local Testing mode, I'm requesting review from @snowflakedb/local-testing
   • I am adding new logging messages
   • I am adding a new telemetry message
   • I am adding new credentials
   • I am adding a new dependency
   • If this is a new feature/behavior, I'm adding the Local Testing parity changes.
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3. Please describe how your code solves the related issue.

   Please write a short description of how your code change solves the related issue.

[sfc-gh-yuwang]

LGTM, please also update changelog before merge, thanks!