fix: caching

[alexander-akait]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

fix:

• weak cache for webpack@4
• keep assets info for webpack@4
• respect immutable info

Breaking Changes

No

Additional Info

We should refactor filename: Function, because it can create wrong filenames in some rare cases (if you return non immutable path - i.e. without [name] or [file] or [path]).

[codecov]

Codecov Report

Merging #194 into master will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #194      +/-   ##
==========================================
+ Coverage   98.72%   98.75%   +0.03%     
==========================================
  Files           4        4              
  Lines         157      161       +4     
  Branches       46       47       +1     
==========================================
+ Hits          155      159       +4     
  Misses          1        1              
  Partials        1        1              

Impacted Files	Coverage Δ
src/Webpack4Cache.js	100.00% <100.00%> (ø)
src/Webpack5Cache.js	100.00% <100.00%> (ø)
src/index.js	98.41% <100.00%> (+0.05%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7fc01f0...e4b410d. Read the comment docs.