[BREAKING CHANGE] Replace `mode` with sub-commands about trippy

[c-git]

Humm if I may share an opinion on this. At first glace it doesn't appear to need to be a breaking change. Isn't it possible to support both (the -m without any args) and the subcommand with args?

[fujiapple852]

@c-git it would be possible, but perhaps not desirable.

The motivation for introducing sub-commands is so that each sub-command can have bespoke arguments without polluting the common argument namespace.

So for example, for the dot report we wish to add some arguments to dictate how it is rendered and these arguments would not make sense for other reports or for the Tui. Likewise the various --tui-xxx arguments do not make sense when running in non-Tui modes but are allowed today. This is essentially applying the classic "make invalid state unrepresentable" guidance to command line arguments.

If we were to preserve the current --mode argument it would, at best, be restricted to specify default arguments for the sub-command.

More generally, until Trippy hits 1.0 it should be considered unstable (technically going from 0.x to 0.x+1 allows for breaking changes in the Cargo semver rules) such that we are not locked into non-optimal design choices prematurely.

Therefore I'd prefer to deprecate (with a runtime warning) and include a prominent notice in the release note.

This may all be moot however, as we can only switch to use sub-commands if we can discover the magic incantations needed to allow clap to make positional arguments mandatory in sub-commands.

[c-git]

Yeah this makes sense. I think it's better to keep it clean.

[fujiapple852]

Putting this on the backlog for now, may revisit the idea in the future.