feat(picker): add `Flag` value type and `Pickable` implementation

Add a new `Flag` enum in `mingling_picker::value` that explicitly
distinguishes between an absent flag (`Inactive`) and a present flag
(`Active`), along with its `Pickable` implementation.  Rename internal
fields from `flag_*` to `arg_*` for consistency, update the default
naming case to `Kebab`, and enable the `mingling_support` feature in
workspace settings.

1 files changed, 1 insertions, 0 deletions

diff --git a/.vscode/settings.json b/.vscode/settings.json
index 3f1ff1d..7472e1c 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -7,4 +7,5 @@
     "mingling_pathf/test/Cargo.toml",
     "mingling_picker/test/Cargo.toml",
   ],
+  "rust-analyzer.cargo.features": ["mingling_support"],
 }