feat: add configurable dispatch_error_module for rebranded chains

Add a new `dispatch_error_module` option to the subxt macro and CodegenBuilder
that allows chains with rebranded runtime modules to specify their own path for
the DispatchError type.

By default, subxt generates:
  pub type DispatchError = runtime_types::sp_runtime::DispatchError;

Chains like Kurdistan SDK (Pezkuwi) that rebrand sp_runtime to pezsp_runtime
can now specify:
  dispatch_error_module = "pezsp_runtime"

This generates:
  pub type DispatchError = runtime_types::pezsp_runtime::DispatchError;

Changes:
- codegen/src/lib.rs: Add dispatch_error_module field to CodegenBuilder
- codegen/src/api/mod.rs: Pass dispatch_error_module to generate_runtime
- codegen/src/api/calls.rs: Use configurable module path for DispatchError
- macro/src/lib.rs: Add dispatch_error_module attribute parsing

macro/src/lib.rs

@@ -56,6 +56,11 @@ struct RuntimeMetadataArgs {
     no_default_substitutions: bool,
     #[darling(default)]
     unstable_metadata: darling::util::Flag,
+    /// The module path for DispatchError (default: "sp_runtime").
+    /// Chains with rebranded runtime modules can use this to specify their path,
+    /// e.g., "pezsp_runtime" for Kurdistan SDK.
+    #[darling(default)]
+    dispatch_error_module: Option<String>,
     #[cfg(feature = "runtime-wasm-path")]
     #[darling(default)]
     runtime_path: Option<String>,
@@ -170,6 +175,11 @@ fn subxt_inner(args: TokenStream, item_mod: syn::ItemMod) -> Result<TokenStream,
         codegen.set_type_substitute(sub.path, sub.with);
     }
 
+    // Set the dispatch error module path if provided:
+    if let Some(dispatch_error_module) = args.dispatch_error_module {
+        codegen.set_dispatch_error_module(dispatch_error_module);
+    }
+
     let code = codegen
         .generate(metadata)
         .map_err(|e| e.into_compile_error())?;