feat(aws-batch): restore unmanagedvCpus after provider support lands

[sakul-learning]

Summary

UnmanagedComputeEnvironmentProps.unmanagedvCpus is part of the AWS CDK API being ported in #136, but the generated @cdktn/provider-aws BatchComputeEnvironmentConfig cannot currently represent it because hashicorp/aws does not expose the AWS Batch API field on aws_batch_compute_environment.

Upstream provider tracking issue:

• [Enhancement]: Support unmanaged_vcpus in aws_batch_compute_environment hashicorp/terraform-provider-aws#49311

Until that provider enhancement is released and regenerated into @cdktn/provider-aws, #136 intentionally fails fast rather than silently accepting a capacity reservation that Terraform would omit.

Current fail-fast locations

At PR head 1c3ac230c3e88f164057e4911ff3d3b5568e56a9:

• Public API deviation notice: src/aws/compute/batch/unmanaged-compute-environment.ts#L43-L50
• Constructor rejection and explanation: src/aws/compute/batch/unmanaged-compute-environment.ts#L120-L136
• Missing L1 forwarding location: src/aws/compute/batch/unmanaged-compute-environment.ts#L156-L185
• Regression test currently expecting the unsupported-input error: test/aws/compute/batch/unmanaged-compute-environment.test.ts

Work once provider support lands

After hashicorp/terraform-provider-aws#49311 is implemented and included in a published AWS Provider release:

1. Upgrade/regenerate @cdktn/provider-aws so BatchComputeEnvironmentConfig exposes the new unmanaged_vcpus field.
2. Remove the constructor ValidationError and the temporary TERRACONSTRUCTS DEVIATION: NOT SUPPORTED documentation.
3. Forward UnmanagedComputeEnvironmentProps.unmanagedvCpus into the generated BatchComputeEnvironment resource configuration.
4. Replace the current fail-fast unit test with synthesis assertions proving the Terraform JSON contains the expected value.
5. Add/update an AWS integration test that performs terraform apply, verifies DescribeComputeEnvironments.unmanagedvCpus, updates the value and verifies it again, then performs terraform destroy and verifies cleanup.
6. Confirm import/refresh does not drift before closing this issue.

Acceptance criteria

• Provider issue [Enhancement]: Support unmanaged_vcpus in aws_batch_compute_environment hashicorp/terraform-provider-aws#49311 is released.
• TerraConstructs uses generated bindings containing unmanaged_vcpus.
• UnmanagedComputeEnvironment({ unmanagedvCpus: N }) synthesizes the corresponding Terraform argument instead of throwing.
• Unit tests cover Terraform rendering.
• A real AWS apply/read/update/read/destroy integration test passes.
• Temporary deviation comments and fail-fast code are removed.