fix: P256 key parity corrections

[mirceanis]

What issue is this PR fixing

Example:
closes #1135
fixes #1136

What is being changed

The way publicKeyHex was computed for Secp256r1 keys was not correct, as the parity prefix was getting removed.
This PR fixes that problem and proposes a method for updating existing keys:
https://github.com/uport-project/veramo/blob/663f4b206ec2470126d5b423340045788dbcb3da/__tests__/data.migration.test.ts#L48

The method still has to be invoked manually, but it should be fairly easy to add just before a createAgent call, since all the other classes(KeyManagementSystem, KeyStore, PrivateKeyStore, encryption keys) and data should be available.

This also updates the JWK utils code that was inventing a parity prefix to the public keys, but would have worked only 50% of the time.

Quality

Check all that apply:

• I want these changes to be integrated
• I successfully ran pnpm i, pnpm build, pnpm test, pnpm test:browser locally.
• I allow my PR to be updated by the reviewers (to speed up the review process).
• I added unit tests.
• I added integration tests.

[codecov]

Codecov Report

Base: 85.17% // Head: 85.27% // Increases project coverage by +0.09% 🎉

Coverage data is based on head (9279d02) compared to base (70ff72e).
Patch coverage: 89.79% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             next    #1137      +/-   ##
==========================================
+ Coverage   85.17%   85.27%   +0.09%     
==========================================
  Files         149      149              
  Lines       15261    15283      +22     
  Branches     1612     1615       +3     
==========================================
+ Hits        12999    13032      +33     
+ Misses       2262     2251      -11     

Impacted Files	Coverage Δ
packages/did-provider-jwk/src/jwkDidUtils.ts	74.13% <78.26%> (+2.17%)	⬆️
...ata-store-json/src/identifier/private-key-store.ts	94.11% <100.00%> (+4.75%)	⬆️
...ges/data-store/src/identifier/private-key-store.ts	92.00% <100.00%> (+4.85%)	⬆️
packages/did-provider-jwk/src/jwk-did-provider.ts	66.41% <100.00%> (ø)
packages/kms-local/src/key-management-system.ts	90.08% <100.00%> (+1.10%)	⬆️

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