Supports deserializing block id in snapshots

[brooksprumo]

Problem

For SIMD 333¹, the block id will be serialized to/deserialized from snapshots. In order to maintain snapshot compatibility between adjacent versions (edge <-> beta, and beta <-> stable), we must be able to deserialize (and ignore) the new field in adjacent versions before we serialize the new field into the snapshot.

Summary of Changes

Add support for deserializing the block id in snapshots.

Note, if the implementation of SIMD 333 is intended for v4.0, then this PR will need to be backported to v3.1.

Additional Testing

• Load a snapshot with this PR that was created by v3.0 (one that does not populate the new block_id field): ✅
• Load a snapshot with this PR that was created by master that does populate the new block_id: ✅

Footnotes

1. https://github.com/solana-foundation/solana-improvement-documents/blob/main/proposals/0333-snapshot-include-block-id.md ↩

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.5%. Comparing base (0e27a67) to head (7367231).
⚠️ Report is 9 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##           master    #9644     +/-   ##
=========================================
- Coverage    82.5%    82.5%   -0.1%     
=========================================
  Files         901      901             
  Lines      323411   323411             
=========================================
- Hits       267096   267075     -21     
- Misses      56315    56336     +21     

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[roryharr]

I assume this default_on_eof makes things compatible if the block_id is not present?

[brooksprumo]

Yep, exactly! I'll add some more info to the PR description with additional testing I've done.