feat: add Block structure models

[archx3]

Introduced new models for Block, BlockSection, BlockRow, BlockColumn, and BlockContent to manage blocks with nested sections, rows, and columns. Ensured each model includes appropriate fields and relationships, with timestamps for creation and updates. The changes increase flexibility for handling complex block layouts.

Summary / Highlights

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• [x] I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• [x] I've tested my changes manually.
• [ ] I've added unit tests to my PR.

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• [ ] I linked this PR to the relevant issue.
• [ ] I moved the linked issue from the "Sprint backlog" to "In progress" when I started this.
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[codecov[bot]]

Codecov Report

Attention: Patch coverage is 31.86813% with 62 lines in your changes missing coverage. Please review.

Project coverage is 56.61%. Comparing base (03dc385) to head (b0e92ca). Report is 25 commits behind head on main.

Files with missing lines	Patch %	Lines
src/_main_/utils/blocks/__init__.py	0.00%	62 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1167 +/- ## ========================================== - Coverage 56.67% 56.61% -0.07% ========================================== Files 473 474 +1 Lines 34834 34925 +91 ========================================== + Hits 19743 19772 +29 - Misses 15091 15153 +62 ```

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