feature: support hyperparameter sweeps

[Saba9]

Add ability to define, launch, and monitor hyperparameter sweeps with trackio. View results in the UI along with parallel coordinates chart.

[akkiyolo]

Hi! I'd like to take a first pass at this.

Given the scope of full sweep support (launch + monitor + parallel coordinates chart) is pretty large, I'm planning to start with the backend piece as a first PR:

trackio.sweep() : define a search space (grid or random) and run it locally by calling a training function once per config
Reuses the existing config and group fields on runs, so sweep runs show up grouped in the dashboard already no schema changes
API shape roughly mirrors wandb's sweep config so existing configs mostly drop in

Not in this first PR (happy to follow up or if someone else wants to pick these up): the parallel-coordinates chart in the dashboard, a CLI launcher for external scripts, and Bayesian search.