fix: massive tests, fixed query param and filter minor bugs

[zoedsoupe]

This pull request introduces significant improvements to the Supabase PostgREST library, focusing on enhanced query building, filter processing, and integration testing. Key changes include the addition of helper functions for headers and query parameters, extended support for complex filter conditions, refactored query-building logic, and comprehensive integration tests to ensure robust functionality.

Enhancements to filter processing:

• lib/supabase/postgrest/filter_builder.ex: Added support for new operators (between, is, in, etc.) and improved handling of complex filter combinations, such as nested conditions and array modifiers.
• test/supabase/postgrest/filter_builder_test.exs: Introduced extensive test coverage for edge cases, additional operators, and integration scenarios to validate the behavior of the process_condition function.

Refactoring query-building logic:

• lib/supabase/postgrest/query_builder.ex: Refactored insert and upsert methods to streamline conflict handling and header/query parameter construction using helper functions. Added maybe_add_conflict_query for cleaner conflict query management. [1] [2]

Addition of helper functions:

• lib/supabase/postgrest/helpers.ex: Introduced get_header and get_query_param utility functions for extracting values from headers and query lists, improving code readability and reducing duplication.
• lib/supabase/postgrest/transform_builder.ex: Integrated Helpers.get_header to simplify header processing in transform operations. [1] [2]

Comprehensive integration tests:

• test/supabase/postgrest/integration_test.exs: Added integration tests to validate complex query chains, transformations, foreign table operations, edge cases, and method-specific behaviors, ensuring the library's reliability in real-world scenarios.