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.mrs

@@ -0,0 +1,11 @@
+// hello.mrs — smoke test
+// Demonstrates: single ident binding, ident construction with #[a => b]
+macro hello! {
+    $name:ident => {
+        T~{
+            pub fn #[say => $name]() -> &'static str {
+                "hello from the macro!"
+            }
+        }
+    }
+}