util: update prefixedHexString to use literal string template

[gabrocheleau]

TypeScript 4.1 introduced template literal types: https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-1.html

We can use those to restrict the type of some strings further with no runtime performance downside. This PR updates PrefixedHexString from string to 0x{string}

[codecov]

Codecov Report

Attention: Patch coverage is 94.44444% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 84.88%. Comparing base (4be68d2) to head (9353778).
Report is 7 commits behind head on master.

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blockchain	?
client	84.88% <94.44%> (-0.04%)	⬇️
common	?
devp2p	?
evm	?
genesis	?
statemanager	?
trie	?
tx	?
util	?
vm	?
wallet	?

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[holgerd77]

Oh, that’s actually a hyper-great one, love this! 🤩🙏❤️

[holgerd77]

(feel that I should really start looking into TypeScript (updates) a bit more, maybe/likely there is other new base functionality we can leverage in a useful and very targeted way. Also, we can actually generally look into updating our Typescript version (what is a bit tricky and what I haven't given much thought yet: what is actually with TypeScript backwards compatibility, so if we update to a new version and use some of the very latest features. Then we likely also break other people's TypeScript code. 🤔 So guess this also needs at least some basic thinking and following guidelines we set for ourselves (maybe in a first round: just not get too hyper-progressive with this stuff and not fully jump on the latest stuff from 2 weeks ago (atm we are not in danger with our 4.7.4 usage from (just googled...) mid 2022. 😂)).

[acolytec3]

LGTM