Add test for update_fee_config NotInitialized path

[Benedict315]

Description

Summary: Adds a test to cover the previously untested NotInitialized error path in the update_fee_config function.

Changes:

Added test_update_fee_config_rejects_not_initialized test in test.rs
The test calls try_update_fee_config before initialize and asserts that it returns Err(Ok(StreamError::NotInitialized))
Context: The update_fee_config function calls load_config(&env) at line 90 in lib.rs, which returns StreamError::NotInitialized when called before initialize. While this error path was already tested once via transfer_admin, there was no specific test calling update_fee_config on an uninitialized contract.

Testing:

Test passes: test_update_fee_config_rejects_not_initialized ... ok
closes #792

[ogazboiz]

meaningful test: try_update_fee_config on an uninitialized contract asserts Err(NotInitialized) not a panic (update_fee_config hits load_config()? before the auth-gated logic), and it's not a duplicate of the existing NotInitialized test. cargo test green (98). merging.