What is the execution timeout for OS Policy ExecResource validate/enforce scripts?

## Context
We are evaluating the use of OS Policy assignments with `ExecResource` for scripts that may involve network calls or long-running operations. We want to understand the agent's behavior around script execution time limits to ensure our scripts complete reliably.
We'd like to understand:

1. **Is there a default timeout** that the OS Config agent enforces on `validate` or `enforce` script execution? (e.g., 5 minutes, 30 minutes, no limit?)
2. **Is this timeout configurable** via the OS Policy assignment spec or agent configuration?
3. **What happens when a script exceeds the timeout** — is the process killed, and what exit code/compliance status is reported?

## What I've Checked

- The [ExecResource API reference](https://cloud.google.com/compute/docs/osconfig/rest/Shared.Types/OSPolicy#ExecResource) does not show a `timeout` field
- The [OS Policy documentation](https://cloud.google.com/compute/docs/os-configuration-management/working-with-os-policies) mentions rollout wait times but not per-script execution timeouts
- I could not find any agent-level configuration for script timeouts in the documentation

## Environment

- OS Config agent (latest)
- Linux (Debian/Ubuntu) and Windows VMs
- ExecResource with inline scripts (`interpreter: SHELL` / `interpreter: POWERSHELL`)

Start with the linked ExecResource API reference and OS Policy documentation, then trace the OS Config agent's ExecResource handling for SHELL and POWERSHELL on Linux and Windows. Confirm whether a timeout is defined or configurable, and document process termination, exit-code, and compliance behavior for scripts that exceed it.

Written by the indexing model from the issue text.