Building with `--features ts-gen` corrupts future builds without it

[brannondorsey]

Describe the bug

Once you've built with --features ts-gen, as is the default used by rust-analyzer in VSCode, future builds without this feature fail. This is because the git tracked src/generated/meshtastic.rs file is modified to require the specta crate, but this dependency is not included with default builds.

To Reproduce
Steps to reproduce:

1. git clone https://github.com/meshtastic/rust.git
2. git submodule update --init
3. cargo build (works)
4. cargo build --features ts-gen
5. cargo build (doesn't work anymore)

Expected behavior

Builds should be idempotent, no matter what features were enabled.

Additional context

This behavior is particularly frustrating for VSCode users, as the first cargo build they try and run will fail if the VSCode editor has already been opened on the project, and a ts-gen build may have been created by the rust-analyzer automatically.

I think the proper fix is to modify build.rs so that src/generated/meshtastic.rs doesn't get permanently modified after the build.

[krant]

Thanks for the bug @brannondorsey , I hope #54 will fix it for you.