Fix psalm issues

Author: alcaeus

psalm-baseline.xml

@@ -135,19 +135,6 @@
       <code>stdClass</code>
     </MoreSpecificReturnType>
   </file>
-  <file src="src/Model/BSONIterator.php">
-    <MixedArgument>
-      <code>$documentLength</code>
-      <code>$documentLength</code>
-      <code><![CDATA[$this->options['typeMap']]]></code>
-    </MixedArgument>
-    <MixedAssignment>
-      <code><![CDATA[$this->position]]></code>
-    </MixedAssignment>
-    <MixedOperand>
-      <code>$documentLength</code>
-    </MixedOperand>
-  </file>
   <file src="src/Model/ChangeStreamIterator.php">
     <MixedArgument>
       <code><![CDATA[$reply->cursor->nextBatch]]></code>

src/Model/BSONIterator.php

@@ -23,7 +23,9 @@
 use MongoDB\Exception\UnexpectedValueException;
 use ReturnTypeWillChange;
 
+use function assert;
 use function is_array;
+use function is_int;
 use function sprintf;
 use function strlen;
 use function substr;
@@ -49,6 +51,7 @@ class BSONIterator implements Iterator
 
     private int $position = 0;
 
+    /** @var array{typeMap: array, ...} */
     private array $options;
 
     /**
@@ -142,6 +145,7 @@ private function advance(): void
         }
 
         [, $documentLength] = unpack('V', substr($this->buffer, $this->position, self::BSON_SIZE));
+        assert(is_int($documentLength));
 
         if ($this->bufferLength - $this->position < $documentLength) {
             throw new UnexpectedValueException(sprintf('Expected %d bytes; %d remaining', $documentLength, $this->bufferLength - $this->position));