windows/arm64 support

### Proposal

Add official support for running Nomad on Windows/ARM64 platforms.

### Use-cases

We are increasingly seeing adoption of ARM64-based Windows devices (e.g., Snapdragon-powered) in enterprise development and internal testing environments. While Linux/ARM64 and macOS/ARM64 are already supported, lack of support for Windows/ARM64 prevents us from running Nomad clients or development setups on these machines.

The goal is to allow Nomad agents (primarily dev/test nodes) to run on Windows ARM64.

### Attempted Solutions

We attempted to build Nomad from source using Go’s native support for GOOS=windows GOARCH=arm64. Although compilation succeeds, it is unclear whether there may be potential runtime issues and missing task driver support (e.g., raw_exec, plugin compatibility).

No files or tests are named. Start by building with GOOS=windows and GOARCH=arm64, then investigate runtime behavior for Nomad agents and the raw_exec and plugin support mentioned in the proposal. Done means Nomad clients and development setups can run on Windows/ARM64 with the relevant task drivers and plugins working.

Written by the indexing model from the issue text.