branch-4.0: [fix](be) Handle legacy DecimalV2 segments with missing precision/frac (#63569)

[jacktengg]

Pick: #63569

Problem Summary: After upgrading from 3.1.4 to 4.0.4, queries on DecimalV2 columns fail with:

[INTERNAL_ERROR]meet invalid precision: real_precision=0,
max_decimal_precision=27, min_decimal_precision=1

Root cause: Segments written by Doris < 2.1.0 (before #26572) do not persist precision/frac in ColumnMetaPB; they default to 0 when read back. Since #35222, DataTypeFactory passes those raw values as original_precision/original_scale into DataTypeDecimalV2, which calls check_type_precision(0) and throws. 3.1.4 was unaffected because the old code hardcoded (27, 9).

Fix: In _create_primitive_data_type for OLAP_FIELD_TYPE_DECIMAL, when precision is not positive (legacy segment), pass UINT32_MAX to DataTypeDecimalV2 to signal that the original precision/scale are unknown. DecimalScaleInfo<TYPE_DECIMALV2> already treats UINT32_MAX as 'unknown' and falls back to the in-memory (27, 9) representation in get_original_precision()/get_original_scale().

Fix "meet invalid precision: real_precision=0" when querying DecimalV2 columns on segments written by Doris versions older than 2.1.0.

• Test: Unit Test
  • Added DataTypeDecimalTest.create_decimalv2_from_legacy_tablet_column covering: legacy TabletColumn (unset precision/frac), modern TabletColumn with decimal(26,6), and legacy segment_v2::ColumnMetaPB with default-0 precision/frac.
• Behavior changed: No
• Does this need documentation: No

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

Release note

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Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

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[jacktengg]

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