feat: design and scaffold backfilling plugin

[georgi-l95]

Description

This PR adds new backfill plugin, which works in two main configurations: Backfill or Continuous.

• Backfill means that it works as a secondary source of blocks with main purpose to fill gaps
• Continuous is a mode, which will be mainly used by Tier 2 operators, because this way, it rock-node will consume blocks mainly from a list of other block-nodes.

Related Issues

• Closes Design and Scaffold Backfilling Plugin #70

Reviewer Checklist

• The code follows the project's coding standards.
• New and existing unit tests pass locally with my changes.
• I have added necessary documentation (if applicable).
• I have confirmed that this change does not introduce any new security vulnerabilities.

[codecov]

Codecov Report

❌ Patch coverage is 89.63039% with 101 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.02%. Comparing base (50fd815) to head (144dd54).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/rock-node-backfill-plugin/src/worker.rs	84.49%	58 Missing ⚠️
crates/rock-node-backfill-plugin/src/lib.rs	89.43%	26 Missing ⚠️
crates/rock-node-persistence-plugin/src/service.rs	81.48%	15 Missing ⚠️
app/rock-node/src/main.rs	0.00%	1 Missing ⚠️
crates/rock-node-persistence-plugin/src/lib.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #109      +/-   ##
==========================================
+ Coverage   64.80%   68.02%   +3.22%     
==========================================
  Files          47       50       +3     
  Lines        6444     7350     +906     
==========================================
+ Hits         4176     5000     +824     
- Misses       2268     2350      +82     

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