## Add Fuzzing Capability to Valkey

### Overview
This PR adds a fuzzing capability to Valkey, allowing developers and
users to stress test their Valkey deployments with randomly generated
commands. The fuzzer is integrated with the existing valkey-benchmark
tool, making it easy to use without requiring additional dependencies.

### Key Features
• **Command Generator**: Automatically generates Valkey commands by
retrieving command information directly from the server
• **Two Fuzzing Modes**:
- normal: Generates only valid commands, doesn't modify server
configurations
- aggressive: Includes malformed commands and allows CONFIG SET
operations

• **Multi-threaded Testing**: Each client runs in a dedicated thread to
maximize interaction between clients and enable testing of complicated
scenarios

• **Integration with valkey-benchmark**: Uses the existing CLI interface

### Implementation Details
• Added new files:
- `fuzzer_command_generator.h/c`: Dynamically generates valkey commands.
- `fuzzer_client.c`: Orchestrate all the client threads, report test
progress, and handle errors.

• Modified existing files:
  - valkey-benchmark.c: Added fuzzing mode options and integration

### Command Generation Approach
The fuzzer dynamically retrieves command information from the server,
allowing it to adapt to different Valkey versions and custom modules.
Since the command information generated from JSON files is sometimes
limited, not all generated commands will be valid, but approximately 95%
valid command generation is achieved.

It is important to generate valid commands to cover as much code path as
possible and not just the invalid command/args path. The fuzzer
prioritizes generating syntactically and semantically correct commands
to ensure thorough testing of the server's core functionality, while
still including a small percentage of invalid commands in `aggressive`
mode to test error handling paths

#### Config modification
For CONFIG SET command, the situation is more complex as the server
currently provides limited information through CONFIG GET *. Some
hardcoded logic is implemented that will need to be modified in the
future. Ideally, the server should provide self-inspection commands to
retrieve config keys-values with their properties (enum values,
modifiability status, etc.).

### Issue Detection
The fuzzer is designed to identify several types of issues:
• Server crashes
• Server memory corruptions / memory leaks(when compiled with ASAN)
• Server unresponsiveness
• Server malformed replies

For unresponsiveness detection, command timeout limits are implemented
to ensure no command blocks for excessive periods. If a server doesn't
respond within 30 seconds, the fuzzer signals that something is wrong.

### Proven Effectiveness
When running against the latest unstable version, the fuzzer has already
identified several issues, demonstrating its effectiveness:
* valkey-io#2111
* valkey-io#2112
* valkey-io#2109
* valkey-io#2113
* valkey-io#2108
* valkey-io#2137
* valkey-io#2106
* valkey-io#2347
* valkey-io#2973
* valkey-io#2974
### How to Use
Run the fuzzer using the valkey-benchmark tool with the --fuzz flag:

```bash
# Basic usage (10000 commands 1000 commands per client, 10 clients)
./src/valkey-benchmark --fuzz -h 127.0.0.1 -p 6379 -n 10000 -c 10

# With aggressive fuzzing mode
./src/valkey-benchmark --fuzz --fuzz-level aggressive -h 127.0.0.1 -p 6379 -n 10000 -c 10

# With detailed logging
./src/valkey-benchmark --fuzz --fuzz-log-level debug -h 127.0.0.1 -p 6379 -n 10000 -c 10
```

The fuzzer supports existing valkey-benchmark options, including TLS and
cluster mode configuration.

---------

Signed-off-by: Uri Yagelnik <[email protected]>