Rename the `core` feature to `mingling_support` in `mingling_picker` and
propagate it through `mingling_picker_macros`.  Add the `is_flag` field
to `PickerTag` to indicate participation in parsing after a `--`
separator.  Remove empty `seek.rs` file.

Define a `core` feature in mingling_picker that gates a new `corebind`
module and re-exports its contents. The module is propagated to the
upstream `mingling` crate under the same feature flag.

Add a configurable `ParserStyle` struct defining option prefix,
separator
and case-sensitivity conventions, with built-in constants for Unix,
PowerShell and Windows styles. Provide a one-time global style setter.

Re-export the new `parselib` module from `mingling_picker` and wire it
through `mingling`'s `picker` facade. Also relocate `Groupped` and
`RenderResult` re-exports in `prelude` for better ordering.

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`.

std::io::Write import

Replace r_println!/r_print! macro usage across all example renderers
with
explicit RenderResult construction using std::io::Write, enabling more
flexible output handling and reducing reliance on macro-side effects.