feat: allow to encode LSP2 Array length only

[CJ42]

What kind of change does this PR introduce (bug fix, feature, docs update, ...)?

feature (wip)

What is the current behaviour (you can also link to an open issue here)?

Currently it is only possible to encode a full array of valueType when the keyType is Array.

What is the new behaviour (if this is a feature change)?

Allow to only encode the Array length only of uint128 that is 16 bytes long, not a full array.

Other information:

[codecov-commenter]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (9640d9f) 83.71% compared to head (d4f51fd) 83.77%.
Report is 19 commits behind head on develop.

Files	Patch %	Lines
src/lib/encoder.ts	75.00%	0 Missing and 5 partials ⚠️
src/lib/getDataFromExternalSources.ts	33.33%	0 Missing and 2 partials ⚠️
src/lib/utils.ts	84.61%	1 Missing and 1 partial ⚠️

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Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #326      +/-   ##
===========================================
+ Coverage    83.71%   83.77%   +0.05%     
===========================================
  Files           18       17       -1     
  Lines         1130     1128       -2     
  Branches       255      259       +4     
===========================================
- Hits           946      945       -1     
+ Misses          98       93       -5     
- Partials        86       90       +4     

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[Hugoo]

What is the status of this?

WIP for a month now. Shall we close it?