refactor: Introduce crates folder (#2088)

This PR introduces a new `crates` directory and moves all "product" crates into that folder. 

Part of #2059.

crates/ruff_macros/src/lib.rs

@@ -0,0 +1,40 @@
+//! This crate implements internal macros for the `ruff` library.
+
+use proc_macro::TokenStream;
+use syn::{parse_macro_input, DeriveInput, ItemFn};
+
+mod config;
+mod define_rule_mapping;
+mod derive_message_formats;
+mod rule_code_prefix;
+mod rule_namespace;
+
+#[proc_macro_derive(ConfigurationOptions, attributes(option, doc, option_group))]
+pub fn derive_config(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+
+    config::derive_impl(input)
+        .unwrap_or_else(syn::Error::into_compile_error)
+        .into()
+}
+
+#[proc_macro]
+pub fn define_rule_mapping(item: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    let mapping = parse_macro_input!(item as define_rule_mapping::Mapping);
+    define_rule_mapping::define_rule_mapping(&mapping).into()
+}
+
+#[proc_macro_derive(RuleNamespace, attributes(prefix))]
+pub fn derive_rule_namespace(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+
+    rule_namespace::derive_impl(input)
+        .unwrap_or_else(syn::Error::into_compile_error)
+        .into()
+}
+
+#[proc_macro_attribute]
+pub fn derive_message_formats(_attr: TokenStream, item: TokenStream) -> TokenStream {
+    let func = parse_macro_input!(item as ItemFn);
+    derive_message_formats::derive_message_formats(&func).into()
+}