Updating rust-bitcoin and supporting musig roadmap

We have a goal to update rust-elements to the latest 1.0 versions of rust-bitcoin crates; relatedly but separately we want to cleanup our APIs, and critically, we want to support musig2.

* [ ] rewrite rust-secp256k1-zkp as a wholly independent library which depends on the latest libsecp256k1-zkp
* [ ] port the rust-secp musig2 PR to rust-secp-zkp, merge it, and release it
* [ ] update rust-elements to use that
* [ ] update rust-elements to use `bitcoin-hashes 1.0`
* [ ] update rust-elements to use `bitcoin-consensus-encoding 1.0` rather than own encoding library) (blocked on https://github.com/rust-bitcoin/rust-bitcoin/pull/6184 I think)
* [ ] update rust-elemnets to use `bitcoin-units 1.0` (not yet released)

先檢視 checklist 中提到的 rust-secp256k1-zkp 獨立化工作與 rust-secp 的 musig2 PR，接著追蹤 rust-elements crate 所需的更新。當 musig2 支援發布，且 rust-elements 使用列出的 1.0 bitcoin crates，同時考量所指出的 upstream 阻礙時，這項工作就完成了。

由索引模型根據 Issue 內容生成。