feat: support immediates

[bartlomieju]

This commit adds support for immediates - they are run after "next ticks" but before "macrotasks"

[littledivy]

Do we need a test?

[codecov-commenter]

Codecov Report

❌ Patch coverage is 72.22222% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.98%. Comparing base (0c7f83e) to head (79d3025).
⚠️ Report is 328 commits behind head on main.

Files with missing lines	Patch %	Lines
core/ops_builtin_v8.rs	50.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1174      +/-   ##
==========================================
- Coverage   81.43%   79.98%   -1.46%     
==========================================
  Files          97      100       +3     
  Lines       23877    25809    +1932     
==========================================
+ Hits        19445    20643    +1198     
- Misses       4432     5166     +734     

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[bartlomieju]

Currently immediates don't support refing/unrefing.