Mark MetricFunctionPtr as doc(hidden)

It has to be pub since it's exposed through the public VectorType trait,
but details of how FFI calls, trampolines etc are handled probably
shouldn't be part of the public API.

Author: tnibler

rust/lib.rs

@@ -481,6 +481,7 @@ pub use ffi::{IndexOptions, MetricKind, ScalarKind};
 /// ```
 ///
 /// In this example, `dimensions` should be defined and valid for the vectors `a` and `b`.
+#[doc(hidden)]
 pub enum MetricFunctionPtr {
     B1X8Metric(*mut std::boxed::Box<dyn Fn(*const b1x8, *const b1x8) -> Distance + Send + Sync>),
     I8Metric(*mut std::boxed::Box<dyn Fn(*const i8, *const i8) -> Distance + Send + Sync>),