[Executino] Chunk data pack pruning config fix

[zhangchiqing]

This PR fixes two issues:

1. When I increase the threshold to retain more chunk data packs, it run into a fatal error, saying the latest is less than next block.

{"level":"fatal",..."error":"failed to create block iterator: failed to create range for block iteration: latest block is less than next block: 242742568 < 245752965","time":"2025-03-03T20:40:39.583143782Z","message":"unhandled irrecoverable error"}

This is resolved by allowing the latest to go backward and even blow the next block to iterate.

2. Report the pruning related metrics on startup, so that the metrics won't report as 0, which causes the dashboard showing some confusing spikes.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 41.22%. Comparing base (3561e2b) to head (d9f9397).

Files with missing lines	Patch %	Lines
module/block_iterator/state.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7112      +/-   ##
==========================================
- Coverage   41.22%   41.22%   -0.01%     
==========================================
  Files        2153     2153              
  Lines      189278   189278              
==========================================
- Hits        78029    78024       -5     
  Misses     104745   104745              
- Partials     6504     6509       +5     

Flag	Coverage Δ
unittests	41.22% <75.00%> (-0.01%)	⬇️

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