Add a new `test-all` command that runs tests across all crates with
optional per-crate command overrides via `mingling-ci.toml` files.

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.

Allow completion functions to omit the context parameter, accept owned
ShellContext or any From<&ShellContext> type, and return any type
implementing Into<Suggest>. Add From<&str> for SuggestItem and derive
Clone for ShellContext.

The legacy `parser` feature and its module tree (`mingling::parser`,
`Argument`, `Picker`, `Pickable`, etc.) have been fully removed and
replaced by the `picker` feature powered by `arg-picker`.

BREAKING CHANGE: Remove `parser` feature and use `picker` instead.
Migration guide: Replace `features = ["parser"]` with
`features = ["picker"]` and update API usage per the provided table.

The `dispatcher!` macro no longer requires a `CMD*` dispatcher type
argument; the dispatcher struct is now generated internally as
`__Dispatcher{Pascal}`. The `Node` type, `node!` macro, and
`Dispatcher::node()` / `clone_dispatcher()` methods are removed.

Dispatchers are now always registered at compile time, removing the
`with_dispatcher` / `with_dispatchers` methods and the
`PathfinderConfig` API. The `dispatch_tree` feature now only controls
the matching strategy (trie vs linear list).

Move the REPL's argument splitting logic into a new public `utils`
module exposing the `ArgumentSplitter` trait for reuse by downstream
code.

Change `HookPreDispatchInfo.arguments` from `&[String]` to `&mut
Vec<String>`
so hooks can rewrite command-line arguments before dispatch.