Feature request: Provide runnable tasks for flake attributes

[vikanezrimaya]

Perhaps it's a bit of a hard thing to implement, but it would be really nice to be able to run my flake checks directly from Zed. Turning the flake.nix's checks attrset into a runnable, as well as potentially marking other flake attributes as runnables, would be nice.

[notpeter]

There are currently two ways that tasks can be detected in Zed:

1. via runnables.scm with tree-sitter. See: example runnables.scm in the zed repo.
2. via LSP experimental/runnables like rust-analyzer does. See: Use lsp runnables  zed-industries/zed#16160