Add CMEK arguments to client.batches.create

[matt-davis27]

Description

Fixes #2622.

Add Customer Managed Encryption Key [CMEK] arguments to client.batches.create (which allows the user to set the keys directly in the configuration of a new batch job)

Summary of Changes

types.py — Added encryption_spec field to both:

• CreateBatchJobConfig(pydantic model) — accepts EncryptionSpec or dict
• CreateBatchJobConfigDict (TypedDict) — accepts EncryptionSpecDict

batches.py — Added mapping in _CreateBatchJobConfig_to_vertex that converts encryption_spec.kms_key_name to encryptionSpec.kmsKeyName on the API request body.

tests/batches/test_create_with_cmek.py — new test file to ensure CMEK arguments are parsed correctly and added to batch job.

Usage

You can now add CMEK to your batch job config in one of two ways:

# Via config
client.batches.create(
    model="gemini-2.5-flash",
    src="gs://bucket/input",
    config=genai.types.CreateBatchJobConfig(
        dest="gs://bucket/output",
        encryption_spec=genai.types.EncryptionSpec(
            kms_key_name="projects/my-project/locations/us-central1/keyRings/my-kr/cryptoKeys/my-key"
        ),
    ),
)

# Via dict shorthand
client.batches.create(
    model="gemini-2.5-flash",
    src="gs://bucket/input",
    config={
        "dest": "gs://bucket/output",
        "encryption_spec": {"kms_key_name": "projects/.../cryptoKeys/my-key"},
    },
)

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