Normalize enum serialization strategy

Some enums are missing the `serde` rename macro (e.g. `SystemSnapshotType`, `SnapshotCompression`), while others use`#[serde(rename_all = "lowercase")]` instead of snake_case.

All enums should use a consistent serialization strategy

Locate the definitions of SystemSnapshotType, SnapshotCompression, and the other enums, then compare their existing serde attributes. Standardize the enum serialization strategy so missing rename attributes and inconsistent lowercase versus snake_case usage are resolved across all enums; done means the enum declarations follow one consistent approach.

Written by the indexing model from the issue text.