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/derive_builder.mrs

@@ -0,0 +1,24 @@
+// derive_builder.mrs — builder pattern generator
+// Demonstrates: struct pattern, variadic field binding, escape block,
+//               expression injection, spread iteration in struct and impl bodies
+macro derive_builder! {
+    struct $name:ident { $($field:ident : $ty:ty),* } => {
+        @{
+            let builder_name = format_ident!("{}_Builder", name.to_string());
+        }
+        T~{
+            pub struct ${ builder_name } {
+                for field in $fields =>
+                    pub $field.name: Option<$field.ty>,
+            }
+            impl ${ builder_name } {
+                pub fn build(self) -> $name {
+                    $name {
+                        for field in $fields =>
+                            $field.name: self.$field.name.unwrap(),
+                    }
+                }
+            }
+        }
+    }
+}