Add more debug info when running into ErrSliceOutOfRange when reading WAL

[ahrtr]

Add more debug info when running into ErrSliceOutOfRange when reading WAL. If the gap between offset and len(ents) is huge, then most likely the WAL record is somehow corrupted, otherwise if it's just +-1, then most likely it's a bug (i.e of the raft).

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.74%. Comparing base (3241803) to head (9143bef).
Report is 4 commits behind head on main.

Additional details and impacted files

Files with missing lines	Coverage Δ
server/storage/wal/wal.go	57.88% <100.00%> (+0.07%)	⬆️

... and 21 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19067      +/-   ##
==========================================
- Coverage   68.75%   68.74%   -0.02%     
==========================================
  Files         420      420              
  Lines       35626    35627       +1     
==========================================
- Hits        24495    24490       -5     
+ Misses       9712     9711       -1     
- Partials     1419     1426       +7     

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ahrtr, serathius

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