Validate dataset primary key identifiers

[bob-codedaptive]

Motivation

• The dataset schema field for a declared primary key (primaryKeyColumn / primary_key_column) was a raw string interpolated into backend CREATE TABLE DDL without being validated, enabling SQL identifier quote-breakout and statement injection.
• The existing identifier validator validateDatasetColumnIdentifier / validate_dataset_column_identifier was already applied to columns and indexes but the primary-key field was omitted across Swift and Rust stores, leaving a high-impact SQL injection surface.

Description

• Apply the existing identifier validation to DatasetSchema.primaryKeyColumn / primary_key_column before any backend/state access in Swift stores: PersistenceKitSQLite/SQLiteDatasetStore.swift, PersistenceKitPostgreSQL/PostgreSQLDatasetStore.swift, and PersistenceKitInMemory/InMemoryDatasetStore.swift.
• Apply the same validation in Rust stores: rust/src/sqlite.rs, rust/src/postgres.rs, and rust/src/dataset_store.rs (InMemory), so the PK name is checked prior to constructing/issuing DDL.
• Add regression tests that assert a double-quote / quote-breaking payload in the declared primary-key name is rejected for the Swift dataset store tests and the Rust SQLite dataset-store tests (DatasetStoreTests.swift and rust/src/sqlite.rs).

Testing

• Ran the focused Rust test cargo test create_dataset_rejects_primary_key_column_with_double_quote and the new Rust unit passed (ok).
• Attempted the Swift test swift test --filter DatasetStoreTests/invalidIdentifier_primaryKeyColumn_sqlInjection_doubleQuote but the run was blocked/failed due to a missing local package dependency (packages/libs/SubstrateTypes), so Swift-side tests could not be executed in this environment.
• Verified repository changes compile and unit-test-suite execution for the Rust crate completed with the new test included (no regressions observed for the exercised checks).

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Codex Task