Don't rebuild proto files if nothing in the proto dir has changed

[fadeev]

Rebuilding proto files takes time, would be great if we could skip the process for when only Go files are changed.

[fedekunze]

ideally building proto files should be disabled and should only run by passing a flag. Otherwise starting the chain takes way longer than necessary

[fadeev]

We're adding a separate command that will generate go from proto: starport generate proto-go, so it can be run manually. Maybe adding starport chain serve --skip-proto makes sense. I would still keep make serve build everything by default, because it's what new developers want: build everything for me with a single command.

[ilgooz]

• Let's try to omit go mod download and check how much time we cut from there.

For proto:

• Calculate a hash from go.mod + proto files in the project, including third party ones defined in the config.yml + isRebuildAll enabled.
• And calculate a hash from the contents and paths of generated files.

If these two hashes are the same between c build executions or when c serve triggered by a file change, automatically skip generating code from proto for go and others enabled through the config.yml.

[ilgooz]

Our last decisions about this future:

• When a proto is changed under the proto/ dir of a chain; we'll check which module has changed and only do code generation for that module.
• When a proto file is changed in one of the third party dirs defined in config.yml: we'll do code generation for all of the modules of the chain (for entire proto/ dir of the chain).
• When the go.mod of the chain has changed; we'll do code generation for the modules imported in go.mod and for the entire proto/ dir of the chain.

also see #1997.