Memoize CallableType::describe() per verbosity level

ObjectType::isSuperTypeOf() keys its cache by describe(VerbosityLevel::cache())
of the other type, so a union of classes with a callable(...) describes the
same CallableType once per class member. Since describe() prints through
TypeNodeDescriber (a PHPDoc node traversal swapping name nodes, then the
printer), that became the bulk of the time for such unions: a file with
1,000 calls of a function taking T|A1|...|A10|callable(A1, A2, A3, A4): T
described 140,000 callables, 7,000 of them distinct.

The description is now cached per level, as ClosureType, UnionType and
IntersectionType already do. The turbo extension mirrors the cache.

Amp-Thread-ID: https://ampcode.com/threads/T-01a1b250-3c08-762d-acb0-9cdf8e7a210e

Author: ondrejmirtes

src/Type/CallableType.php

@@ -79,6 +79,9 @@ class CallableType implements CompoundType, CallableParametersAcceptor
 
 	private Assertions $assertions;
 
+	/** @var array<int, string> */
+	private array $cachedDescriptions = [];
+
 	/**
 	 * @api
 	 * @param list<ParameterReflection>|null $parameters
@@ -335,7 +338,7 @@ public function equals(Type $type): bool
 
 	public function describe(VerbosityLevel $level): string
 	{
-		return $level->handle(
+		return $this->cachedDescriptions[$level->getLevelValue()] ??= $level->handle(
 			static fn (): string => 'callable',
 			function (): string {
 				$assertedParameterNames = [];