refactor: use hash instead mtime for cache key

[PeachScript]

使用 content hash 作为缓存键，替代原有的 mtime，这样 CI 环境也可以将 cache 复用

顺便修正了 bundle 模块源码中的变量名，由于不影响用户使用就不新开 PR 处理了，Close #709

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (b8a7a79) 94.39% compared to head (0411b4d) 94.39%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #718   +/-   ##
=======================================
  Coverage   94.39%   94.39%           
=======================================
  Files          55       55           
  Lines        1551     1553    +2     
  Branches      369      367    -2     
=======================================
+ Hits         1464     1466    +2     
+ Misses         87       82    -5     
- Partials        0        5    +5     

Files Changed	Coverage Δ
src/builder/bundle/index.ts	100.00% <100.00%> (ø)
src/builder/bundless/loaders/index.ts	80.95% <100.00%> (+0.46%)	⬆️
src/doctor/parser.ts	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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