test: configure vimeo/psalm to verify type inference

This is mostly to include type inference in regression tests: out-of-the
box type inference for 99% of usages is based on
`TreeMapper#map(class-string<T>, mixed): T`, and it is worth preserving
that behavior without the need of plugins.

This test covers that.

psalm.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0"?>
+<psalm
+    errorLevel="1"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xmlns="https://getpsalm.org/schema/config"
+    xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
+>
+    <projectFiles>
+        <directory name="tests/StaticAnalysis" />
+        <ignoreFiles>
+            <directory name="vendor" />
+        </ignoreFiles>
+    </projectFiles>
+</psalm>

tests/StaticAnalysis/Stub/A.php

@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+
+namespace CuyZ\Valinor\Tests\StaticAnalysis\Stub;
+
+final class A
+{
+}

tests/StaticAnalysis/can-infer-tree-mapper-results.php

@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace CuyZ\Valinor\Tests\StaticAnalysis;
+
+use CuyZ\Valinor\Mapper\TreeMapper;
+use CuyZ\Valinor\Tests\StaticAnalysis\Stub\A;
+
+/** @param mixed $input */
+function mappingClassWillInferObjectOfSameType(TreeMapper $mapper, $input): A
+{
+    return $mapper->map(A::class, $input);
+}