feat: builder for unsigned contract call

[hstove]

fixes #125. cc @kyranjamie . I'm building this for the Stacks Wallet, so we can sign Stacking transactions with a hardware wallet.

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Description

Adds makeUnsignedContractCall function. This is built to be almost identical to the makeUnsignedStacksTokenTransfer function, which can accept one or more public keys. The actual makeContractCall, similarly, uses the unsigned variant to build the transaction, and then it simply signs the TX.

Type of Change

• [x] New feature
• [ ] Bug fix
• [ ] API reference/documentation update
• [ ] Other

Checklist

• [x] Code is commented where needed
• [x] Unit test coverage for new or modified code paths
• [x] npm run test passes
• [ ] Changelog is updated
• [x] Tag 1 of @yknl, @zone117x, @reedrosenbluth for review

[codecov[bot]]

Codecov Report

Merging #131 into master will decrease coverage by 0.40%. The diff coverage is 51.85%.

@@            Coverage Diff             @@
##           master     #131      +/-   ##
==========================================
- Coverage   83.31%   82.90%   -0.41%     
==========================================
  Files          28       28              
  Lines        2163     2182      +19     
  Branches      446      447       +1     
==========================================
+ Hits         1802     1809       +7     
- Misses        357      369      +12     
  Partials        4        4              

Impacted Files	Coverage Δ
src/builders.ts	68.29% <51.85%> (-1.94%)	:arrow_down:

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[agraebe]

pinging @yknl for migration of this to the monorepo once merged

[yknl]

Closing since this has been moved to the stacks.js repo.