Support datetime expressions in weather-sp output templates

[zeel2104]

Summary

Fixes #535.

Adds support for richer Python-style expressions in weather-sp output templates, including datetime formatting expressions like {datetime.strptime(f"{time}", "%H%M").strftime("%H:%M:%S")}.

This allows an output template such as:

gs://test-output/splits/test-file_{date}-{datetime.strptime(f"{time}", "%H%M").strftime("%H:%M:%S")}.grib

to produce:

gs://test-output/splits/test-file_20200101-12:00:00.grib

Changes

• Added expression-aware output template parsing/evaluation in OutFileInfo.
• Updated split-dimension detection so variables used inside expressions, such as time, are included.
• Adjusted GribSplitterV2 to use raw split-dimension temp filenames for grib_copy, then apply the richer Python formatter during upload.
• Added tests for datetime expression formatting and split-dimension extraction.

Testing

Manual validation passed:

['date', 'time']

gs://test-output/splits/test-file_20200101-12:00:00.grib

Full pytest was not run locally because this Windows Python 3.14 environment is missing pygrib/ecCodes support.

[mahrsee1997]

@zeel2104, can you please fix lint issue, thanks!

[zeel2104]

@mahrsee1997

Thanks for pointing it out! I fixed the lint issue by wrapping the long datetime output template in the test file and pushed the update.

[shail-parekh]

Instead of using a complex AST-based parser, can we implement a simple native wrapper for date and time that preserves the raw GRIB date/time field formats by default?

[shail-parekh]

With this approach, if a pipeline is initiated with an output-template using double quotes or without quotes, it can cause the pipeline to fail. We should handle these scenarios as well.

[shail-parekh]

we can simplify the codebase by removing this class and helper methods, as we can remove the AST based approach!

[shail-parekh]

Please update formatted_output_path to use native Python string formatting.