feat: add BnB algorithm for coin selection

[Cyrix126]

fix: #3

Make BnB the default algorithm to select coins. Fall back to the older one if it doesn't find a solution.

Note for v5: the only thing to change would be the locktime parameter from int to Locktime type.

[MatthewLM]

@Cyrix126 Thank you for this. This would be excellent to include in v5.0.0 so rebasing to v5.0.0 would be ideal. Unfortunately I'm not sure when I'll get chance to fully review and then I'm not sure when I can finish v5.0.0 which is blocked by two things. The first thing is Windows support #37. The second thing is that there is memory corruption when using MuSig2 with WASM.

I might release v5.0.0 without Windows support (unless I can get help confirming Windows works OK) and I might make MuSig2 unavailable for web.

[MatthewLM]

The unit tests fail on the web target due to the call depth of the search function. Can the algorithm be made non-recursive?

[Cyrix126]

I rewrote the part that was using recursion. That will fix the wasm build.

[MatthewLM]

@Cyrix126 Sorry for the delay in getting to this. When I get time, I will look over in detail, hopefully soon. I may merge this into a new branch for a 4.2.0 release. The BnB algorithm would not be default for 4.2.0 to avoid a breaking change, but I can make it the default for 5.0.0.