refactor(dataset-store): make DatasetKind enum private to crate

[LNSD]

Encapsulate DatasetKind as a private implementation detail to prevent viral dependencies across the codebase. External crates now use RawDatasetKind with extractor-specific zero-sized type markers (EvmRpcDatasetKind, SolanaDatasetKind, FirehoseDatasetKind, DerivedDatasetKind) and equality comparisons instead of pattern matching.

• Make DatasetKind enum pub(crate) in dataset-store
• Add FromStr to RawDatasetKind for CLI argument parsing
• Add PartialEq implementations between extractor kinds and RawDatasetKind
• Replace DatasetKind with RawDatasetKind in public APIs (error types, handlers)
• Replace pattern matching with equality comparisons throughout callers

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Note

Encapsulates DatasetKind inside dataset-store and migrates all public-facing APIs to RawDatasetKind with extractor marker types for comparisons.

• Make DatasetKind pub(crate); drop its serde impls/macros and keep local parsing/Display utilities
• Add FromStr for RawDatasetKind and implement PartialEq bridges with EvmRpcDatasetKind, SolanaDatasetKind, FirehoseDatasetKind, DerivedDatasetKind
• Replace DatasetKind with RawDatasetKind across errors, provider APIs (ProviderInfo), scheduler/worker (JobDescriptor), dump, and controller
• Refactor ampctl manifest generate to accept RawDatasetKind, branch via marker-type equality, and add Solana generation; update error messaging
• Update admin-api handlers to use marker-type equality for manifest validation/registration; tweak error text and OpenAPI docs
• Add Solana manifest fixture and new integration tests; remove old CLI manifest test

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