feat: add custom loader support

[whxaxes]

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

[codecov-io]

Codecov Report

Merging #41 into master will increase coverage by 1.6%.
The diff coverage is 96.29%.

@@            Coverage Diff            @@
##           master      #41     +/-   ##
=========================================
+ Coverage   95.86%   97.47%   +1.6%     
=========================================
  Files          14       16      +2     
  Lines         508      594     +86     
  Branches       62       73     +11     
=========================================
+ Hits          487      579     +92     
+ Misses         11        4      -7     
- Partials       10       11      +1

Impacted Files	Coverage Δ
src/generators/auto.ts	100% <100%> (ø)	⬆️
src/index.ts	97.45% <100%> (+1.16%)	⬆️
src/generators/plugin.ts	100% <100%> (+9.52%)	⬆️
src/generators/object.ts	100% <100%> (ø)	⬆️
src/config.ts	100% <100%> (ø)
src/generators/egg.ts	100% <100%> (ø)	⬆️
src/generators/class.ts	97.72% <100%> (+0.05%)	⬆️
src/generators/config.ts	97.61% <100%> (+0.05%)	⬆️
src/scripts/eggInfo.ts	100% <100%> (ø)	⬆️
src/watcher.ts	100% <100%> (ø)	⬆️
... and 8 more

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[whxaxes]

1.24.0