Implement Fuzz testing

The [CNCF Fuzzing Initiative](https://github.com/cncf/cncf-fuzzing) in collaboration with [OSS-Fuzz](https://github.com/google/oss-fuzz) provides a fuzzing infrastructure that enables CNCF projects to leverage **coverage-guided continuous fuzzing.** [Envoy Proxy](https://github.com/envoyproxy/envoy/tree/main/test/fuzz) already benefits from extensive fuzz testing, so applying the same approach to Envoy Gateway will ensure similar robustness and reliability.

### Tasks

#### Develop initial set of fuzz tests

- [x] #5426
- [x] #5428
- [x] #5462
- [x] https://github.com/envoyproxy/gateway/pull/5904

#### Integrate Continuous Fuzzing with OSS-Fuzz

- [x] #5492
- [x] #5501
- [x] #5502

### References

1. Fuzzing library [Go-fuzz](https://github.com/dvyukov/go-fuzz)
2. Fuzzing Infrastructure: [OSS-Fuzz](https://github.com/google/oss-fuzz)
3. Best Practices: [OSS-Fuzz ideal integration](https://google.github.io/oss-fuzz/advanced-topics/ideal-integration/)

### Ongoing discussions and PR in OSS-Fuzz

- [ ] https://github.com/google/oss-fuzz/issues/13285
- [ ] https://github.com/google/oss-fuzz/issues/13393
- [ ] https://github.com/google/oss-fuzz/issues/13263
- [ ] https://github.com/google/oss-fuzz/issues/13236
- [ ] https://github.com/google/oss-fuzz/issues/13211
- [ ] https://github.com/google/oss-fuzz/pull/13220
- [ ] https://github.com/google/oss-fuzz/pull/13333

### Important Links

- [OSS-Fuzz dashboard for envoy-gateway](https://oss-fuzz.com/testcases?project=gateway&open=yes)
- **Closing Note and Future works:** [Integrating CNCF Fuzzing Framework for Envoy Gateway (2025 Term 1) - LFX Mentorship](https://gist.github.com/sudiptob2/29552cbf9e1adb2a6e81e0cb7ffa2b07)