feat: use quansync to support async transformer and on-demand loading.

[antfu]

WIP

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[netlify]

❌ Deploy Preview for shiki-next failed.

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[codecov]

Codecov Report

Attention: Patch coverage is 98.93617% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.15%. Comparing base (ece4b02) to head (717f88d).

Files with missing lines	Patch %	Lines
packages/core/src/highlight/code-to-hast.ts	98.86%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #960      +/-   ##
==========================================
+ Coverage   95.13%   95.15%   +0.01%     
==========================================
  Files          88       88              
  Lines        7365     7391      +26     
  Branches     1525     1536      +11     
==========================================
+ Hits         7007     7033      +26     
  Misses        352      352              
  Partials        6        6              

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