refactor!: replace build.rs with compile-time macro build steps

BREAKING CHANGE: Replace the `build`/`builds` feature system with
compile-time macro-driven generation. `gen_program!()` now automatically
invokes `build_comp!()` and `build_pathf!()` when the `comp`/`pathf`
features are enabled, eliminating the need for `build.rs` and
`[build-dependencies]` blocks.

This removes the `build` feature, the `mingling::build` module, and all
related build-time API functions. Completion scripts are now written to
`{target_directory}/mingling/` instead of `target/release/`. The
`mingling_cli` uses `build_comp!("mling")` for its custom binary name.

1 files changed, 6 insertions, 0 deletions

diff --git a/mingling_pathf/src/error.rs b/mingling_pathf/src/error.rs
index 5a748c4..bd850a8 100644
--- a/mingling_pathf/src/error.rs
+++ b/mingling_pathf/src/error.rs
@@ -53,6 +53,11 @@ pub enum MinglingPathfinderError {
         /// Details from the parser about the parse failure.
         message: String,
     },
+
+    /// `cargo metadata` could not be executed or parsed.
+    ///
+    /// `message` contains the underlying error from the cargo invocation.
+    CargoMetadata(String),
 }
 
 impl fmt::Display for MinglingPathfinderError {
@@ -82,6 +87,7 @@ impl fmt::Display for MinglingPathfinderError {
             Self::SynError { path, message } => {
                 write!(f, "Failed to parse {}: {message}", path.display())
             }
+            Self::CargoMetadata(message) => write!(f, "cargo metadata failed: {message}"),
         }
     }
 }