CLI - spacetime generate always deletes stale files

[bfops]

Description of Changes

spacetime generate --delete-files deletes all files in the target directory that start with the SpacetimeDB autogenerated file header. This PR makes turns that behavior permanently on, and removes the flag.

We think this is unlikely to negatively affect users, since it only deletes files that start with the header that is automatically generated by SpacetimeDB. If users do experience negative effects, we can add a flag to disable this behavior.

API and ABI breaking changes

Yes. We no longer support --delete-files.

Expected complexity level and risk

2

Testing

$ cargo run -- generate --lang csharp --out-dir $WORK/my_new_project/ --project-path $WORK/my_new_project/
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.23s
     Running `target/debug/spacetime generate --lang csharp --out-dir /home/lead/work/clockwork/my_new_project/ --project-path /home/lead/work/clockwork/my_new_project/`
Saving config to /home/lead/.spacetime/config.toml.
info: component 'rust-std' for target 'wasm32-unknown-unknown' is up to date
checking crate with spacetimedb's clippy configuration
    Checking spacetime-module v0.1.0 (/mnt/nutera/work/my_new_project)
    Finished `release` profile [optimized] target(s) in 0.15s
    Finished `release` profile [optimized] target(s) in 0.07s
Optimising module with wasm-opt...
Could not find wasm-opt to optimise the module.
For best performance install wasm-opt from https://github.com/WebAssembly/binaryen/releases.
Continuing with unoptimised module.
Build finished successfully.
compilation took 2.092558726s
Generate finished successfully.

$ cp $WORK/my_new_project/AddReducer.{cs,cs.stale}

$ cargo run -- generate --lang csharp --out-dir $WORK/my_new_project/ --project-path $WORK/my_new_project/
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.23s
     Running `target/debug/spacetime generate --lang csharp --out-dir /home/lead/work/clockwork/my_new_project/ --project-path /home/lead/work/clockwork/my_new_project/`
Saving config to /home/lead/.spacetime/config.toml.
info: component 'rust-std' for target 'wasm32-unknown-unknown' is up to date
checking crate with spacetimedb's clippy configuration
    Checking spacetime-module v0.1.0 (/mnt/nutera/work/my_new_project)
    Finished `release` profile [optimized] target(s) in 0.14s
    Finished `release` profile [optimized] target(s) in 0.07s
Optimising module with wasm-opt...
Could not find wasm-opt to optimise the module.
For best performance install wasm-opt from https://github.com/WebAssembly/binaryen/releases.
Continuing with unoptimised module.
Build finished successfully.
compilation took 2.110778341s
The following files were not generated by this command and will be deleted:
  /home/lead/work/clockwork/my_new_project/AddReducer.cs.stale
Are you sure you want to delete these files? [y/N]y
Files deleted successfully.
Generate finished successfully.

[jdetter]

@bfops Yeah hold on I think there are some bugs here. We only prompt users after we've already done the generation? That seems wrong to me. Also we should only be replacing files which contain our special header, not just overwriting whatever file is already there. Can we fix those issues here or do you want to do a separate PR?

[bfops]

Let's do those things in a separate PR since they're not API-breaking.
Also, it looks like we have the capacity to generate files in subdirectories, but it's not clear to me that we can delete them from subdirectories..

[bfops]

Created #1786

[jdetter]

I'm approving this - we're fixing the other existing issues in a separate PR