Add examples with cargo run --example support

- Move .mrs files into misses-compiler/examples/ alongside .rs runners
- Add lib.rs exposing parse/codegen for use by example binaries and main.rs
- Fix parser: #[attr] vs #[a => b] disambiguation (look for => before ])
- Fix parser: `for` keyword in `impl Foo for Bar` no longer triggers spread
  (is_spread_for lookahead: must match `for <ident> in $<ident> =>`)
- Add derive_getters.mrs: getter methods via spread iteration
- Add make_id_type.mrs: newtype u64 wrapper with From impls, derive attrs

Run with: cargo run --example hello|derive_builder|declare_table|derive_getters|make_id_type

https://claude.ai/code/session_01Tppkab4eLsL21asHGjQJoF

misses-compiler/examples/hello.rs

@@ -0,0 +1,24 @@
+fn main() {
+    let src = include_str!("hello.mrs");
+    show("hello.mrs", src);
+}
+
+fn show(name: &str, src: &str) {
+    let bar = "=".repeat(60);
+    println!("{bar}");
+    println!("SOURCE  {name}");
+    println!("{bar}");
+    println!("{}", src.trim());
+    println!();
+
+    match misses::parse(src) {
+        Err(e) => eprintln!("parse error: {e}"),
+        Ok(ast) => {
+            let generated = misses::codegen(&ast);
+            println!("{bar}");
+            println!("GENERATED");
+            println!("{bar}");
+            println!("{}", generated.trim());
+        }
+    }
+}