no_std compatible implementation of bitcoin dependencies

[mgravitt]

no_std Support and Contingency

Of course, the pallet requires compilation to WASM, which means support for no_std. This requires changes to all three of the above libraries, each of which already has bitcoindevkit/bdk#205.

The heavy lifting for this has mostly been completed, but the libraries with the updates have not been released yet. Our first preference is to use them directly with their latest release.

However, if they are not released in time, we will either a) build a custom library, or b) host native Rust services as an off-chain worker.

Both of these are temporary solutions, and we would later revert to mainline when the release is available.