Consider combining some of the github action files

[jbesraa]

Currently we add each new action to a new file in workflows. I think we should consider combining some of those flows into a single file.

For example: test.yaml, rust-msrv.yaml, semver-check.yaml, lockfiles.yaml, fmt.yaml, clippy-lint.yaml can probably be combined into a single file

[jbesraa]

Consider running each job with twice once with rust 1.75(our MSRV) and once with rust stable, beside the MSRV check job which should run just with 1.75. This will make sure we always build on rust stable which is usually what people work with, and with our MSRV that we promise not to break.