Add AssuranceTypeMapper for IDE-readable type narrowing

Generate IDE-readable narrowing PHPDoc from a node's #[Assurance] /
fluent mixins narrow types after assert()/check() without a PHPStan extension.

- New AssuranceTypeMapper maps each assurance shape to a Chain<T> generic:
  concrete types, the argument-derived forms (from: Value -> @param T;
  from: TypeString -> @param class-string<T>), element forms, Container
  subjects, and the Wrap/Container/Elements prefix compositions (with union
  de-duplication). #[AssuranceParameter] selects which argument carries the
  type (any position, default first) -- it no longer implies class-string;
  `from` decides the derivation. Argument-wrapping forms stay Chain<mixed> to
  avoid retyping Validator parameters to Chain<T> (which would reject raw,
  non-fluent validators).
- New NarrowingDoc and TerminalMethod value objects; InterfaceConfig gains
  emitNarrowing / chainType / templateParam / terminalMethods, threaded
  through MethodBuilder and MixinGenerator.
- Unit coverage per bucket plus a MixinGenerator narrowing integration test.

Author: alganet

.gitattributes

@@ -0,0 +1,11 @@
+/* export-ignore
+
+# Project files
+/README.md -export-ignore
+/composer.json -export-ignore
+/src -export-ignore
+
+# SBOM information
+/LICENSE -export-ignore
+/LICENSES -export-ignore
+/REUSE.toml -export-ignore

composer.json

@@ -4,6 +4,8 @@
     "keywords": ["respect", "fluentgen", "mixin", "fluent"],
     "type": "library",
     "license": "ISC",
+    "minimum-stability": "dev",
+    "prefer-stable": true,
     "authors": [
         {
             "name": "Respect/FluentGen Contributors",
@@ -20,7 +22,7 @@
         "phpstan/phpstan-strict-rules": "^2.0",
         "phpunit/phpunit": "^12.5",
         "respect/coding-standard": "^5.0",
-        "respect/fluent": "^2.0"
+        "respect/fluent": "3.0.x-dev"
     },
     "suggest": {
         "respect/fluent": "Enables #[Composable] prefix composition support"
@@ -50,5 +52,10 @@
         "allow-plugins": {
             "dealerdirect/phpcodesniffer-composer-installer": true
         }
+    },
+    "extra": {
+        "branch-alias": {
+            "dev-ide-narrowing": "2.1.x-dev"
+        }
     }
 }