fix: Add Ajv type coercion for Express 5 query parameter compatibility

[elaine-mattos]

Description

This PR addresses query parameter type handling changes introduced by Express 5. (see #1340)

Express 5 introduced a breaking change where req.query is now a read-only getter instead of a writable property. This means that custom middleware can no longer reassign req.query to convert types, causing schema validation to fail when expecting any type but a string.

The solution uses Ajv's built-in coerceTypes feature to handle type conversion during schema validation.

Changes made

1 - Enabled Ajv type coercion: allows for automatic type conversion of query string values;
2 - Removed custom querystring middleware and its tests: no longer needed since Ajv handles type coercion;