correct errors and enhance readability in protocol/design-rationale (…

…#290)

* docs: protocol section; spacing

* docs: clarify protocol design philosophy

* docs: fix grammatical errors

* docs: rewrite Accounts over UTXOs

* docs: improve MPT and Verkle section

* docs: improve Hunt for Finality section

* reprhase + typo

* nit:

* note on simplicity

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Co-authored-by: rahul <[email protected]>
Co-authored-by: Mário Havel <[email protected]>