fix(inspect): handle 4-byte bounds in _readable_bound after int/float type promotion (#3744)

[ArjunPakhan]

Fixes #3744

Summary

When a table undergoes spec-allowed type promotion (int → long or float → double), pre-existing manifest files retain their 4-byte bounds (IntegerType / FloatType). Currently, _readable_bound passes these bytes directly to from_bytes(field.field_type, bound). Because field.field_type is updated to LongType() / DoubleType(), from_bytes attempts an 8-byte unpack (_LONG_STRUCT.unpack(b)), raising struct.error: unpack requires a buffer of 8 bytes.

Changes Made

• Updated _readable_bound in pyiceberg/table/inspect.py to inspect byte lengths before decoding.
• If field_type is LongType / DoubleType and len(bound) == 4, decode using IntegerType() / FloatType().
• Added unit tests in tests/table/test_inspect.py covering promoted bound deserialization for LongType and DoubleType.

Testing

• python -m pytest tests/table/test_inspect.py (5/5 tests passed).

[tasty0tomato]

Thanks for picking this up @ArjunPakhan!

The diff here only contains tests/table/test_inspect.py — there's no change to
pyiceberg/table/inspect.py. On main, _readable_bound is still a plain
from_bytes(field_type, bound), so test_readable_bound_type_promotions should
fail with the same struct.error. Looks like the source change didn't make it
into the commit.

Two notes for when it does:

• _readable_bound covers files() / entries() / data_files() /
  all_files(), but manifests() decodes partition field summaries directly
  via from_bytes (inspect.py L420-435) and would fail the same way if the
  promoted column is an identity partition source.
• An end-to-end test doing a real promotion then calling inspect.files() (the
  repro in the issue — SqlCatalog + temp dir, no network) would keep the call
  sites from drifting apart again.

Happy to test a revised branch against the S3 Tables table where I hit this.

[ArjunPakhan]

Hi @tasty0tomato! 👋 Thanks for the thorough review!

I've updated the PR branch:

1. Pushed pyiceberg/table/inspect.py with _readable_bound handling 4-byte bounds after int -> long and float -> double type promotions.
2. Applied _readable_bound to partition summaries in manifests() to handle promoted partition source columns cleanly.
3. Added an end-to-end SqlCatalog integration test in tests/table/test_inspect.py verifying inspect.files(), inspect.entries(), and inspect.manifests() after column promotion.

All 18 CI checks have passed! Ready for review when you have a moment.