fix: ignore already loaded js module

[fraidev]

Fixes: denoland/deno#30688

Summary

Deno currently panics when the same JavaScript module is loaded more than once, which can easily happen when using the --preload flag.

For example:

deno run --preload ./main.ts main.ts

What this PR does

This PR updates the module loading logic to ignore modules that have already been loaded, preventing duplicate imports and avoiding the panic.

Other Runtimes

Both Bun (--preload) and Node.js (--import) already handle this case by skipping already loaded modules.

[CLAassistant]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.77419% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.73%. Comparing base (0c7f83e) to head (2b5f902).
⚠️ Report is 357 commits behind head on main.

Files with missing lines	Patch %	Lines
core/modules/map.rs	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1221      +/-   ##
==========================================
- Coverage   81.43%   79.73%   -1.71%     
==========================================
  Files          97      100       +3     
  Lines       23877    26077    +2200     
==========================================
+ Hits        19445    20792    +1347     
- Misses       4432     5285     +853     

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