feat(microvm): wire MicroVM provider in multi-runner module

[edersonbrilhante]

Description

Integrates the Lambda MicroVM compute provider into the experimental multi-runner and runner-config contracts on top of #5362.

• Adds global and per-lane compute_provider.aws.microvm configuration and precedence resolution.
• Dispatches MicroVM lanes through runner-config while preserving the existing EC2 path.
• Adds MicroVM validation, outputs, documentation, and provider-aware runner-config tests.
• Keeps MicroVM lanes out of EC2 runner-binary synchronization.

Test Plan

• Preserved the tested integration commits from feat(multi-runner): integrate Lambda MicroVM provider #5349; no implementation changes were introduced while creating this independent branch.
• git diff --check passed.
• No live AWS deployment was performed.

Related Issues

• Source PR: feat(multi-runner): integrate Lambda MicroVM provider #5349.
• Depends on independent baseline PR feat(microvm): add standalone Terraform provider baseline #5362.

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None