feat: support immediates

[bartlomieju]

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

[codecov-commenter]

Codecov Report

:x: Patch coverage is 72.22222% with 5 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 80.28%. Comparing base (0c7f83e) to head (1e710fc). :warning: Report is 380 commits behind head on main.

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

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1174      +/-   ##
==========================================
- Coverage   81.43%   80.28%   -1.16%     
==========================================
  Files          97      105       +8     
  Lines       23877    27367    +3490     
==========================================
+ Hits        19445    21971    +2526     
- Misses       4432     5396     +964     

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[bartlomieju]

Currently immediates don't support refing/unrefing.

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