feat: add API to read file slice from base file and list of log files

[yunchipang]

Description

Implements a new API that allows reading a file slice by providing a base file path and a list of log file paths.

existing 2 options to read file slices:

• read_file_slice_by_base_file_path: base file only (no log files)
• read_file_slice: requires pre-built FileSlice object (automatic log discovery)

This new read_file_slice_from_paths API allows users to manually specify which log files to include with a base file.

closes #402

How are the changes test-covered

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

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.57%. Comparing base (150eeef) to head (f19d652).

Files with missing lines	Patch %	Lines
crates/core/src/file_group/reader.rs	50.00%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #446      +/-   ##
==========================================
- Coverage   88.90%   88.57%   -0.34%     
==========================================
  Files          49       49              
  Lines        2713     2739      +26     
==========================================
+ Hits         2412     2426      +14     
- Misses        301      313      +12     

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