### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

It seems like whenever I open a connection to `localhost:4566` (4566 being exposed from the localstack container), for the next ~1 second any HTTP calls will have delayed responses. If I open 10 connections, the delay will be 10 seconds.

### Expected Behavior

Multiple connections can be opened and don't impact other requests until a certain connection limit.

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

1. run localstack: `docker run --rm -it -p 4566:4566 --name ls localstack/localstack:0.14.0` - I managed to reproduce it with versions as old as 0.12.0
2. run something like this to see how long curls take inside the container: 

```bash
docker exec -it ls /bin/bash

# inside the container:
while true; do time curl localhost:4566; sleep 0.1; done
```

3. open connections with telnet:

```
telnet localhost 4566
```

4. observe extended response times in the curl loop. For me it's ~1s extra per open connection (I'm simulating opening more connections with a JVM application opening sockets as I request).

### Environment

```markdown
- OS: macOS / ubuntu, tried both x86 and arm64 macs, and an arm64 linux
- LocalStack: 0.12.0, 0.13.1, 0.14.0
```


### Anything else?

This surfaces itself as extremely slow responses whenever you have e.g. a JVM application that keeps a cached connection pool. Even 10 connections in a pool are enough to cause consistent delays every couple seconds (which I think is after the connections are closed due to the defaults on my client), under no additional traffic targeting localstack.
if region and region.startswith("us-gov-"):
            return "aws-us-gov"
        elif region and region.startswith("us-iso-"):
            return "aws-iso"
        elif region and region.startswith("us-isob-"):
            return "aws-iso-b"
        elif region and region.startswith("cn-"):
            return "aws-cn"
        elif region and re.match(r"^(us|eu|ap|sa|ca|me|af)-\w+-\d+$", region):
            return "aws"
        else:
            raise ArnPartitionRewriteListener.InvalidRegionException(
                f"Region ({region}) could not be matched to a partition."
            )
    @staticmethod
    def _post_process_response_headers(response: RoutingResponse) -> None:
        """Adjust potential content lengths and checksums after modifying the response."""
        if response.headers and response.content:
            if "Content-Length" in response.headers:
                response.headers["Content-Length"] = str(len(to_bytes(response.content)))
            if "x-amz-crc32" in response.headers:
                response.headers["x-amz-crc32"] = calculate_crc32(response.content)
T = TypeVar("T", bound="RegionBackend")
class RegionBackend: