docs: improve apply_precompile documentation (#106)

Added comprehensive documentation for the apply_precompile method that explains
its behavior for adding, updating, and removing precompiles.

Key improvements:
- Clarified that the method applies a transformation to existing precompiles
- Explained the closure's input (Option<precompile>) and output behavior
- Added clear examples for common use cases:
  - Adding a new precompile
  - Updating an existing precompile
  - Removing a precompile
  - Conditional operations
- Documented that returning None removes the precompile
- Documented that returning Some inserts or replaces the precompile

This makes the method's behavior much clearer, especially the fact that
it can be used to remove precompiles by returning None from the closure.

Author: mattsse

crates/evm/src/precompiles.rs

@@ -72,7 +72,44 @@ impl PrecompilesMap {
         dyn_precompiles.inner = new_map;
     }
 
-    /// Applies a new precompile at the given address.
+    /// Applies a transformation to the precompile at the given address.
+    ///
+    /// This method allows you to add, update, or remove a precompile by applying a closure
+    /// to the existing precompile (if any) at the specified address.
+    ///
+    /// # Behavior
+    ///
+    /// The closure receives:
+    /// - `Some(precompile)` if a precompile exists at the address
+    /// - `None` if no precompile exists at the address
+    ///
+    /// Based on what the closure returns:
+    /// - `Some(precompile)` - Insert or replace the precompile at the address
+    /// - `None` - Remove the precompile from the address (if it exists)
+    ///
+    /// # Examples
+    ///
+    /// ```ignore
+    /// // Add a new precompile
+    /// precompiles.apply_precompile(&address, |_| Some(my_precompile));
+    ///
+    /// // Update an existing precompile
+    /// precompiles.apply_precompile(&address, |existing| {
+    ///     existing.map(|p| wrap_with_logging(p))
+    /// });
+    ///
+    /// // Remove a precompile
+    /// precompiles.apply_precompile(&address, |_| None);
+    ///
+    /// // Conditionally update
+    /// precompiles.apply_precompile(&address, |existing| {
+    ///     if let Some(p) = existing {
+    ///         Some(modify_precompile(p))
+    ///     } else {
+    ///         Some(create_default_precompile())
+    ///     }
+    /// });
+    /// ```
     pub fn apply_precompile<F>(&mut self, address: &Address, f: F)
     where
         F: FnOnce(Option<DynPrecompile>) -> Option<DynPrecompile>,