feat(scan): support create index readers with field name during scan process

[lszskye]

feat(scan): support create index readers with field name during scan process

Purpose

Linked issue: #5

Tests

GlobalIndexTest

API and Format

virtual Result<std::vector<std::shared_ptr>> CreateReaders(const std::string& field_name) const = 0;

[Copilot]

Pull request overview

This PR adds support for creating multiple index readers for a field by name during the scan process. The new API method CreateReaders(const std::string& field_name) complements the existing CreateReader method by returning all available index readers for a given field, regardless of index type.

Key Changes:

• Added public API method CreateReaders(const std::string& field_name) to retrieve all index readers for a field
• Refactored internal implementation to extract common logic into a private CreateReaders(const DataField&) method
• Added comprehensive test validating the new API with multiple index types (bitmap and lumina)

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
include/paimon/global_index/row_range_global_index_scanner.h	Added public virtual method CreateReaders(const std::string& field_name) with documentation
src/paimon/core/global_index/row_range_global_index_scanner_impl.h	Added public override for CreateReaders(const std::string&) and private helper CreateReaders(const DataField&)
src/paimon/core/global_index/row_range_global_index_scanner_impl.cpp	Implemented new public method and refactored existing CreateReaders(int32_t) to use common CreateReaders(const DataField&) helper
test/inte/global_index_test.cpp	Added TestScanIndexWithTwoIndexes test case verifying the new API works with bitmap and lumina indexes, and returns empty vector for non-indexed fields

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[lxy-9602]

+1