Add checksum column for reference range table

[btmonier]

Description

• Adds reference range sequence checksum column (rr_checksum) to RList return from getRefRangesFromGraph() method
  • This is used in rPHG2 and returned as a GRanges object for enhanced querying in R.

Type of change

What type of changes does your code introduce? Put an x in boxes that apply.

• [ ] CHANGE (fix or feature that would cause existing functionality to not work as expected)
• [ ] FEATURE (non-breaking change which adds functionality)
• [ ] BUGFIX (non-breaking change which fixes an issue)
• [x] ENHANCEMENT (non-breaking change which improves existing functionality)
• [ ] NONE (if none of the other choices apply. Example, tooling, build system, CI, docs, etc.)

Checklist:

• [x] I have performed a self-review of my code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have updated relevant documentation

Changelog entry

Please add a one-line changelog entry below. This will be copied to the changelog file during the release process.

Add checksum column for getRefRangesFromGraph() return object (rPHG2 functionality)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 80.30%. Comparing base (1c9cf7f) to head (35125a4). Report is 2 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #256 +/- ## ======================================= Coverage 80.29% 80.30% ======================================= Files 84 84 Lines 5928 5929 +1 Branches 1034 1034 ======================================= + Hits 4760 4761 +1 Misses 785 785 Partials 383 383 ```

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