Proof function util helpers refactor

[scorbajio]

This change is an alternative approach to the work started in #3538. It looks into refactoring the trie class to remove proof functionality from the main class and move them into standalone functions in order to improve tree shaking for the trie package and decrease bundle size.

[scorbajio]

Using a minimal code path for the Trie class:

import { Trie } from '@ethereumjs/trie'

const t = new Trie()
console.log(t.root())

Results:

before: 223.6kb
after: 205.7kb
delta: -17.9kb

[acolytec3]

Looks great overall. Some comments need cleanup and I think we can remove that fromProof function entirely.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (fb50628) to head (61e98d9).
Report is 15 commits behind head on master.

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Flag	BASE (fb50628)	HEAD (61e98d9)
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[acolytec3]

LGTM

[holgerd77]

@scorbajio Nice, looks super clean now! 😄

Results are also meaningful (so the -18KB), since this already helps the Block package upwards, and there reduction on this level definitely already counts in! 👍