Use GH Actions caches to reduce CI run times

[sr-gi]

Run times for CI jobs in GH Actions will drastically increase after merging #65. The main reason is twofold:

• First, cln needs to be compiled from source to run the tests, given it needs to be configured with developer flags.
• Second, the tests use teosd, so it needs to be installed in the system (cargo install).

This adds almost twice as much time to run CI checks (~10min -> ~20min).

We could try to use caches to store the compiled cln binaries and see if we can also store a cache from the cargo build of teos from the previous CI jobs. That way we could link the debug teos binaries and we won't need to install them from scratch.

[mariocynicys]

hmmm, I tried the cln plugin on my system and didn't need to enable cln's developer flags. Did this type of dependency come from the E2E tests?

[sr-gi]

@meryacine yes, the E2E test use the dev_sign_last_tx cln rpc command, which is only available if compiled with dev flags.

[sr-gi]

Closed by #65