Extract ClickStack scalar enums

[sdairs]

Closes #378

Summary

• Extract 104 ClickStack scalar enums into a private vocabulary module.
• Move every associated Display/default implementation and preserve all 336 known values, 325 explicit Serde renames, and data-carrying catch-alls.
• Keep ClickStack structs, aliases, and discriminated unions in the model facade for the final library layer.
• Preserve public paths and byte-identical analyzer enum inventory.

Tests

• cargo fmt --all
• cargo check --workspace --all-features
• cargo test -p clickhouse-cloud-api -p clickhouse-openapi-analyzer
• cargo clippy -p clickhouse-cloud-api -p clickhouse-openapi-analyzer --all-targets -- -D warnings

[Copilot]

Pull request overview

This PR extracts the ClickStack scalar enum vocabulary out of the models.rs facade into a dedicated models/clickstack_enums.rs module, while preserving the existing public re-export paths (clickhouse_cloud_api::... and clickhouse_cloud_api::models::...) and keeping enum wire values/catch-alls intact.

Changes:

• Introduces src/models/clickstack_enums.rs containing the extracted ClickStack scalar enums (including their Display/Default behavior and unknown-value catch-alls).
• Wires the new module into src/models.rs via mod clickstack_enums; and pub use clickstack_enums::*;, removing the inlined enum block from the facade.
• Extends the model facade path-stability test to cover ClickStackChartColor as a representative ClickStack enum.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
crates/clickhouse-cloud-api/src/models/clickstack_enums.rs	New module holding extracted ClickStack scalar enums and their implementations.
crates/clickhouse-cloud-api/src/models.rs	Registers + re-exports the new module and removes the extracted inline enum definitions.
crates/clickhouse-cloud-api/tests/model_facade_test.rs	Adds an assertion that ClickStackChartColor keeps identical root vs models:: paths.

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[iskakaushik]

LGTM