feat: add `HudiFileGroupReader` with consolidated APIs to read records

[xushiyan]

Description

• Add FileGroupReader with APIs to read file slices
• Migrate existing APIs to use FileGroupReader

How are the changes test-covered

• [ ] N/A
• [x] Automated tests (unit and/or integration tests)
• [ ] Manual tests
  • [ ] Details are described below

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 91.30435% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.81%. Comparing base (2ef9557) to head (72ca4d7). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/core/src/file_group/reader.rs	92.85%	1 Missing :warning:
crates/core/src/table/mod.rs	80.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #164 +/- ## ========================================== + Coverage 89.16% 89.81% +0.65% ========================================== Files 16 17 +1 Lines 877 884 +7 ========================================== + Hits 782 794 +12 + Misses 95 90 -5 ```

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