lib: Migrate musig2 impl from Sanket's to upstream secp PR branch

Steven Rooserequested to merge
gh-8d0098b3/275/unknown/refs/pull/275/head into master

Migrate our musig2 implemention to the PR branch to upstream rust-secp256k1 that is likely going to be merged at some point.

Fixes https://codeberg.org/ark-bitcoin/bark/issues/270 somehow.

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