Azure SDK migration for kv store

[ChihweiLHBird]

Closes #3021.

Summary

This PR migrates spin-key-value-azure from the legacy Azure Cosmos SDK to the current azure_data_cosmos / azure_core / azure_identity stack.

It updates the Cosmos client construction and item APIs, keeps the existing account-key auth flow, and switches the no-key path to explicit Azure AD credential selection compatible with azure_identity 1.0.

What Changed

• Upgraded spin-key-value-azure to azure_data_cosmos 0.34, azure_core 1.0, and azure_identity 1.0.
• Reworked Cosmos client creation to use AccountReference, async container client initialization, and SDK-managed routing.
• Added optional region runtime config and defaulted it to East US when omitted.
• Replaced the old ambient-auth path with explicit AAD credential selection via auth_type.
• Added support for selecting managed identity by client_id.
• Updated CRUD, batch, increment, and CAS operations to the new SDK APIs.
• Removed the old custom connection-pooling feature and direct reqwest transport setup now that the SDK manages transport internally.

Runtime Config

Existing account-key configuration continues to work unchanged.

For AAD-based auth, this PR supports these auth_type values when key is omitted:

• developer_tools
• managed_identity
• workload_identity
• service_principal

developer_tools is the default when auth_type is omitted. client_id is only used with managed_identity to select a user-assigned identity.

[ChihweiLHBird]

This change is a regression due to the removal of azure_identity::create_default_credential() in the new SDK.
Azure/azure-sdk-for-rust#2093
Azure/azure-sdk-for-rust#4541

I am still evaluating solution to not bring the regression. So marked this PR as a draft.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Modernizes the Azure Cosmos-backed key-value store to use newer Azure SDK APIs and adds explicit Azure AD authentication options plus region-aware routing.

Changes:

• Migrates Cosmos DB interactions from older CollectionClient/document APIs to ContainerClient item APIs with lazy client initialization.
• Adds explicit Azure AD credential selection (auth_type + optional client_id) and optional region configuration for proximity-based routing.
• Updates Azure SDK dependency versions and removes the old connection-pooling feature wiring.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 6 comments.

File	Description
crates/key-value-azure/src/store.rs	Refactors Cosmos client initialization + CRUD/CAS operations to new SDK APIs; adds auth parsing/utilities and unit tests.
crates/key-value-azure/src/lib.rs	Extends runtime config with region, auth_type, and client_id; wires them into store construction and exports AzureCredentialKind.
crates/key-value-azure/Cargo.toml	Updates Azure SDK dependencies to newer major versions; removes old connection-pooling feature block.

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