Move CI and local testing to cargo-rbmt

[luisschwab]

https://github.com/rust-bitcoin/rust-bitcoin-maintainer-tools/tree/master/cargo-rbmt#lock-files

We maintain a Cargo-minimal.lock for MSRV and a Cargo-recent.lock for the stable toolchain, generated via:

cargo rbmt lock

Then we can drop the annoying ci/pin-msrv.sh script.

[luisschwab]

This also makes feature parity between CI and local testing easy.

[Davidson-Souza]

ConceptACK

Do you plan to make this or should I take a shot?

[luisschwab]

I'm PRing with this all over, see:

• Move CI and local testing to cargo-rbmt bitcoindevkit/bdk-bitcoind-client#39
• Migrate CI to cargo-rbmt luisschwab/bdk-floresta#82

I could start doing this here in a few hours, but you can do it if you want

[Davidson-Souza]

Since you already did it multiple times, feel free to open here as well. No hurry.