[feature](be) Add FileScannerV2 native reader

[Gabriel39]

What problem does this PR solve?

Issue Number: None

Related PR: None

Problem Summary: FileScannerV2 did not support Doris Native files. This change adds a native v2 FileReader implementation instead of wrapping the legacy NativeReader. The reader validates the Native header, reads serialized PBlock payloads, caches and replays the first block for schema probing, exposes nullable file-local schema, projects requested columns, and applies file-local filters. Shared materialized-column filtering is also used by JSON and delimited text readers so predicate accounting stays consistent. WAL is intentionally not implemented on the v2 path because current group commit WAL scans are load scans and FileScanOperator only selects FileScannerV2 when src_tuple_id does not resolve to an input tuple.

Release note

None

Check List (For Author)

• Test:
  • Style check: build-support/check-format.sh
  • Unit Test: not run locally because sandbox execution cannot write .git/modules for submodule setup and cannot download datasketches-cpp; the attempted run-be-ut command failed before compiling tests.
• 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

None

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.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

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