`Ec2Client` from `AwsEc2.aws()` is never closed; AWS SDK v2 connections leak in `StartsInstance` and `TerminatesInstance`

What happens

In src/main/java/com/rultor/agents/aws/AwsEc2.java, the method aws() builds and returns a fresh Ec2Client on every invocation:

public Ec2Client aws() {
    return Ec2Client.builder()
        .region(Region.of(this.region))
        .credentialsProvider(StaticCredentialsProvider.create(
            AwsBasicCredentials.create(this.key, this.secret)
        ))
        .build();
}

software.amazon.awssdk.services.ec2.Ec2Client (AWS SDK v2) extends SdkAutoCloseable. Each instance owns an Apache or Netty HTTP client, a thread pool, and a connection pool, and the SDK documentation explicitly states clients are expensive and must be closed.

The two call sites in the same package never close the returned client:

• StartsInstance.java:161-162 — this.api.aws().runInstances(request)
• TerminatesInstance.java:47 — this.api.aws().terminateInstances(...)

Each agent tick that starts or terminates an EC2 instance therefore leaks one full AWS SDK client. Over a long-running rultor deployment that processes many builds, the leaked threads and connection pools accumulate.

What should happen

Either cache a single Ec2Client as a field on AwsEc2 and reuse it across calls (the SDK v2 client is thread-safe), or wrap each call site in a try-with-resources:

try (Ec2Client client = this.api.aws()) {
    client.runInstances(request);
}

The choice depends on how @Immutable is intended to constrain AwsEc2. Either fix eliminates the per-call leak.