This commit introduces a fuzz test for the `Decode` function in the `trix` package. This test immediately uncovered a critical out-of-memory (OOM) vulnerability.
- Adds a new fuzz test, `FuzzDecode`, to `pkg/trix/fuzz_test.go` to continuously test the `Decode` function with a wide range of malformed inputs.
- Fixes a denial-of-service vulnerability where a malicious input could specify an extremely large header length, causing the application to crash due to an out-of-memory error.
- Introduces a `MaxHeaderSize` constant (16MB) and a check in the `Decode` function to ensure that the header length does not exceed this limit.
- Adds a new error, `ErrHeaderTooLarge`, to provide clear feedback when the header size limit is exceeded.
