feat: implement bigint support

[glevco]

Depends on #720

Motivation

See https://github.com/HathorNetwork/internal-issues/issues/363.

This PR adds the necessary structures to support bigint fields, however it does not yet change the OutputValueType to bigint.

Acceptance Criteria

• Implement bigIntToBytes() and remove signedIntToBytes() support for 8 bytes.
• Implement unpackToBigInt() and remove unpackToInt() support for 8 bytes.
• Update bytesToOutputValue() to use unpackToBigInt().
• Dependencies:
  • Added json-bigint and zod.
  • level-transcoder was added explicitly but was already an indirect dependency.
  • Removed long.
• Create api/txApi and api/wallet Zod schemas, updating requests to use transformJsonBigIntResponse().
• Update Output.valueToBytes() to use bigIntToBytes() instead of signedIntToBytes().
• Create Zod schemas for some necessary interfaces.
• Use Zod parsing in WS history txs.
• Update LevelDB sublevels to use jsonBigIntEncoding() where necessary.
• Implement utils/bigint.ts.
• Change WS handler to use JSONBigInt.parse() instead of JSON.parse().
• Change TS target to es2020 instead of es2018, adding support for bigint.

Security Checklist

• Make sure you do not include new dependencies in the project unless strictly necessary and do not include dev-dependencies as production ones. More dependencies increase the possibility of one of them being hijacked and affecting us.

[codecov]

Codecov Report

Attention: Patch coverage is 89.61039% with 8 lines in your changes missing coverage. Please review.

Project coverage is 80.56%. Comparing base (1b31680) to head (6c44af7).

Files	Patch %	Lines
src/api/wallet.ts	50.00%	3 Missing ⚠️
src/utils/bigint.ts	88.23%	2 Missing ⚠️
src/utils/storage.ts	33.33%	2 Missing ⚠️
src/utils/buffer.ts	95.65%	1 Missing ⚠️

Additional details and impacted files

@@                        Coverage Diff                        @@
##           refactor/typing-improvements     #728       +/-   ##
=================================================================
+ Coverage                         66.52%   80.56%   +14.04%     
=================================================================
  Files                                78       82        +4     
  Lines                              6156     6209       +53     
  Branches                           1337     1353       +16     
=================================================================
+ Hits                               4095     5002      +907     
+ Misses                             1985     1195      -790     
+ Partials                             76       12       -64     

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