Make sure we reference the right versions of crates, Rust and tools (besides Cargo.toml)

[bjoernQ]

We have a couple of places where we reference versions

• MSRV in the (not merged yet) tools version check
• That hint about where to look for examples in the generated main
• espflash / probe-rs versions in the tools version check

Ideally, we can get the MSRV from the Cargo.toml

Not sure about espflash and probe-rs - while users should use a recent version, they might get away with something older that works 🤷‍♂ but we should make sure we suggest a version we know will work