feat(picker): add core trait, types, and builder macro for argument

parsing

Implement the foundational `mingling_picker` library along with its
companion
`mingling_picker_macros` crate. The picker provides:

- `Pickable` trait for parsing types from raw strings
- `PickerResult` enum modeling parse outcomes
- `Picker` struct for storing and indexing command-line arguments
- `PickerRequirement` struct for declarative parameter definitions
- `PickerPattern` family (1..32) of typed pattern structs via the
  `internal_repeat` proc macro
- `req!` proc macro as a succinct builder for `PickerRequirement`

Re-export `mingling_picker::macros::*` from the `mingling` crate when
the
`picker` feature is enabled, replacing the previous wildcard re-export
of
`mingling_macros`.

1 files changed, 39 insertions, 0 deletions

diff --git a/mingling_picker/src/pickable.rs b/mingling_picker/src/pickable.rs
new file mode 100644
index 0000000..9fe2c9d
--- /dev/null
+++ b/mingling_picker/src/pickable.rs
@@ -0,0 +1,39 @@
+use crate::PickerResult;
+
+mod implements;
+
+/// A trait for types that can be constructed from a raw string representation.
+///
+/// Implementing this trait allows a type to be "picked" or parsed from a string,
+/// enabling deserialization or configuration loading from textual input.
+///
+/// # Requirements
+///
+/// - The implementing type must be [`Sized`] and implement [`Default`].
+/// - The [`pick`] method performs the actual parsing and may fail.
+///
+/// # Errors
+///
+/// Returns a [`PickerResult`] which encapsulates either a successful parse
+/// or an error indicating why the input could not be parsed.
+///
+/// # Examples
+///
+/// ```
+/// # use mingling_picker::{Pickable, PickerResult};
+/// #[derive(Default)]
+/// struct MyType(String);
+///
+/// impl Pickable for MyType {
+///     fn pick(raw_str: &str) -> PickerResult<Self> {
+///         PickerResult::Parsed(MyType(raw_str.to_string()))
+///     }
+/// }
+/// ```
+pub trait Pickable
+where
+    Self: Sized + Default,
+{
+    /// Parses a `Self` value from the given raw string input.
+    fn pick(raw_str: &str) -> PickerResult<Self>;
+}