Add support for musig() key expressions

[bigspider]

Closes: #208

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 83.33333% with 12 lines in your changes missing coverage. Please review.

Project coverage is 84.63%. Comparing base (6367fb2) to head (dc99225). Report is 4 commits behind head on develop.

Files	Patch %	Lines
src/common/wallet.c	82.60%	12 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #230 +/- ## =========================================== - Coverage 84.73% 84.63% -0.10% =========================================== Files 17 17 Lines 2181 2226 +45 =========================================== + Hits 1848 1884 +36 - Misses 333 342 +9 ``` | [Flag](https://app.codecov.io/gh/LedgerHQ/app-bitcoin-new/pull/230/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LedgerHQ) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/LedgerHQ/app-bitcoin-new/pull/230/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LedgerHQ) | `84.63% <83.33%> (-0.10%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LedgerHQ#carryforward-flags-in-the-pull-request-comment) to find out more.

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[sonarcloud[bot]]

Quality Gate failed

Failed conditions
7.0% Coverage on New Code (required ≥ 80%)
11.1% Duplication on New Code (required ≤ 3%)
E Reliability Rating on New Code (required ≥ A)

See analysis details on SonarCloud

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