[BUG] FIXED: Potential sequence length bug in preprocessed record (Obvious but Critical)

[Chetansahney]

Reference Issues/PRs

Fixes #2265

What does this implement/fix? Explain your changes.

This PR fixes sequence-length metadata in tslib preprocessing.
_preprocess_data() was using len(series) (number of keys in the record) instead of the true time dimension length.
It now sets length from the timestep/sequence length, so downstream logic receives correct series length metadata.

What should a reviewer concentrate their feedback on?

• Correctness of the length calculation change in _preprocess_data()
• Any downstream assumptions that depend on processed["length"]
• Backward compatibility for existing tslib data flows

Did you add any tests for the change?

Yes. Added/updated a regression assertion in test_preprocess_data to verify processed["length"] == len(original_sample["t"]).

Any other comments?

This is a targeted bugfix with minimal surface-area changes.

PR checklist

• The PR title starts with either [ENH], [MNT], [DOC], or [BUG]. [BUG] - bugfix, [MNT] - CI, test framework, [ENH] - adding or improving code, [DOC] - writing or improving documentation or docstrings.
• Added/modified tests
• Used pre-commit hooks when committing to ensure that code is compliant with hooks. Install hooks with pre-commit install. To run hooks independent of commit, execute pre-commit run --all-files

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@818a84d). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...h_forecasting/data/tests/test_tslib_data_module.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2266   +/-   ##
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  Coverage        ?   86.92%           
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  Files           ?      166           
  Lines           ?     9766           
  Branches        ?        0           
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  Hits            ?     8489           
  Misses          ?     1277           
  Partials        ?        0           

Flag	Coverage Δ
cpu	86.92% <0.00%> (?)
pytest	86.92% <0.00%> (?)

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[Chetansahney]

Hi @christy @rustyconover @szepeviktor @TKlerx .
Am looking forward for your reviews :)