feat: acess previous blocks' data in block script using prev_blocks

[stravo1]

Now all prev blocks' block data is accessible to their child blocks through the prev_blocks dictionary.

Example:

[codecov]

Codecov Report

❌ Patch coverage is 61.53846% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.49%. Comparing base (476dbf1) to head (c18a286).
⚠️ Report is 18 commits behind head on develop.

Files with missing lines	Patch %	Lines
builder/utils.py	63.63%	4 Missing ⚠️
...ilder/builder/doctype/builder_page/builder_page.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #533      +/-   ##
===========================================
- Coverage    63.52%   63.49%   -0.04%     
===========================================
  Files           27       27              
  Lines         2794     2802       +8     
===========================================
+ Hits          1775     1779       +4     
- Misses        1019     1023       +4     

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[github-actions]

🎉 This PR is included in version 1.23.0 🎉

The release is available on GitHub release

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