Enhance LLM configuration and installation scripts for improved flexibility

- Added new environment variables in `env.example` and `gpu-rent.vars.example` for fine-tuning LLM settings, including CUDA build options and model version pinning.
- Updated `llm.md` documentation to include detailed descriptions of new configuration options and usage cases for LLM setups.
- Enhanced the `provision.py` script to forward new environment variables during remote installations, improving the installation process for LLM components.
- Modified the `install_llamacpp.sh` script to support conditional CUDA builds and asset URL overrides, ensuring better compatibility with various environments.
- Improved logging in the installation scripts to provide clearer feedback during the setup process.

src/gpu_rent/ssh_ops.py

@@ -323,7 +323,9 @@ def run_script_sudo(
             fh.write(script)
         sftp.chmod(remote_path, 0o755)
         sftp.close()
-        env_s = " ".join(f"{key}={value}" for key, value in (env or {}).items())
+        env_s = " ".join(
+            f"{key}={shlex.quote(str(value))}" for key, value in (env or {}).items()
+        )
         prefix = f"sudo -n env {env_s} " if env_s else "sudo -n "
         command = f"{prefix}bash {remote_path}"
         _stdin, stdout, stderr = client.exec_command(command, timeout=timeout, get_pty=True)