SNOW-3152139: Create UDF_init_once decorator in python client

[sfc-gh-nirsharma]

SNOW-3152139: Create UDF_init_once decorator in python client

What
Adds the udf_init_once decorator to snowflake.snowpark.functions, providing a client-side definition that matches the server-side _snowflake.udf_init_once API.
Why
The @udf_init_once decorator allows users to mark zero-argument functions for one-time execution during pre-fork initialization on Snowflake workers. Initialized state (e.g., loaded models, computed lookup tables) is shared across all workers via Copy-On-Write. This avoids redundant initialization in each worker process.

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.
   • I acknowledge that I have ensured my changes to be thread-safe. Follow the link for more information: Thread-safe Developer Guidelines
   • If adding any arguments to public Snowpark APIs or creating new public Snowpark APIs, I acknowledge that I have ensured my changes include AST support. Follow the link for more information: AST Support Guidelines

3. Please describe how your code solves the related issue.

Added the udf_init_once decorator in snowflake.snowpark.functions for marking functions to be executed once during pre-fork initialization on Snowflake workers, matching the server-side _snowflake.udf_init_once API.

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[sfc-gh-nirsharma]

I have read the CLA Document and I hereby sign the CLA

[sfc-gh-gshe]

LGTM

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.53%. Comparing base (809b627) to head (75fd593).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4269   +/-   ##
=======================================
  Coverage   95.52%   95.53%           
=======================================
  Files         171      171           
  Lines       44360    44368    +8     
  Branches     7577     7579    +2     
=======================================
+ Hits        42377    42385    +8     
  Misses       1221     1221           
  Partials      762      762           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.