Check for unbalanced|nested braces #9

templated urls cannot have unbalanced braces. i.e.

https://www.server/{version} is allowed
https://www.server/{version is not

templated urls also cannot nest braces. i.e.

https://www.server/{version}/{platform} is allowed
https://www.server/{version{platform}} is not

Currently Membrane-core checks this in each ExtractPathParameters implementation:

https://github.com/membrane-php/membrane-core/blob/dcb21bc53aba3463e74212b136a647776192eada/src/OpenAPI/ExtractPathParameters/PathParameterExtractor.php#L25-L39

https://github.com/membrane-php/membrane-core/blob/dcb21bc53aba3463e74212b136a647776192eada/src/OpenAPI/ExtractPathParameters/PathMatcher.php#L30-L40

Currently OpenAPI Router does not check this, but it would be handy for users to know.

Logic should be moved from membrane-core to the openapi-reader.

Not 100% sure if it counts as an "invalid OpenAPI" to have unbalanced braces but it's certainly not helpful for routing and parsing in the rest of Membrane.