fix: panic with concurrent schema parsing

[YousefHagag]

Issue: #481

This pull request introduces a new test for concurrent schema parsing, adds a method to merge schema caches, and updates the schema parsing logic to utilize an internal cache. The most important changes are as follows:

Testing Enhancements:

• concurrent_parse_test.go: Added a new test TestConcurrentParse to validate concurrent schema parsing by running multiple goroutines that parse a test schema. This ensures the thread-safety and correctness of the parsing function.

Schema Cache Enhancements:

• schema.go: Added a new method AddAll to the SchemaCache struct, which allows merging all schemas from one cache into another. This is useful for combining schema caches without duplicating entries.

Schema Parsing Logic Enhancements:

• schema_parse.go: Updated the ParseBytesWithCache function to use an internal SchemaCache for intermediate parsing steps. This change helps in isolating the parsing process and then merging the results back into the original cache, improving the modularity and maintainability of the code.