Add `mingling_pathf` sub-crate and `pathf` feature for automatic
resolution of Mingling type module paths at build time. Scans source
files, identifies macro invocations via pattern matchers, and generates
mapping files consumed by `gen_program!()`.

guidelines

Add four new resource types for common directory paths and a
convenience setup struct that registers all of them at once.

Support `&mut T` resource parameters in async chain functions by using
an extract-store pattern that avoids holding mutable borrows across
await
points. Remove the previous compile-time rejection of this combination.

Introduce `StructuralData` sealed trait and `pack_structural!` /
`group_structural!` / `derive(StructuralData)` macros to control
structured rendering separately from grouping. `Groupped` no longer
requires `Serialize`.