fix: Allow C4 Dynamic multiple interactions

[aristotelos]

C4 Dynamic allows for multiple interactions
between the same components. Before, a second
interaction was merged with the previous
interaction, which was incorrect.

📑 Summary

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Resolves #7183

📏 Design Decisions

The parser cannot determine if relations are duplicate and should be merged easily because the c4Type is not parsed. Therefore do not merge relations in the database. If we want to keep merging relationships for other C4 diagram types, that could be solved in the renderer.

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🦋 Changeset detected

Latest commit: 848b1ee

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commit: 848b1ee

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 3.56%. Comparing base (39d070f) to head (848b1ee).

Files with missing lines	Patch %	Lines
packages/mermaid/src/diagrams/c4/c4Db.js	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #7219   +/-   ##
=======================================
  Coverage     3.56%   3.56%           
=======================================
  Files          473     473           
  Lines        47566   47561    -5     
  Branches       734     734           
=======================================
  Hits          1696    1696           
+ Misses       45870   45865    -5     

Flag	Coverage Δ
unit	3.56% <0.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
packages/mermaid/src/diagrams/c4/c4Db.js	0.00% <0.00%> (ø)

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Build	Status	Details	Updated (UTC)
default (Inspect)	✅ No changes detected	-	Dec 5, 2025, 7:07 AM