feat(ext): add ClickHouse support

[timveil]

Companion to #445 (new database support). Highest effort / most caveats of the candidates — filed for completeness; recommend tackling after the embedded DBs.

Why

ClickHouse is the leading open-source (Apache 2.0) OLAP/columnar database, very widely adopted for analytics. Driver: com.clickhouse:clickhouse-jdbc. Container: org.testcontainers:clickhouse.

Architectural mismatch to resolve first

ClickHouse is not a constraint-enforcing OLTP store, which collides with several of Bloviate's assumptions:

• No FK / PK uniqueness enforcement (MergeTree ORDER BY is not a unique key). Bloviate's FK dependency-graph fill still runs, but there are effectively no FKs to order and no uniqueness guarantees — decide what "filling" means here.
• Insert/engine semantics differ (MergeTree, large batch inserts, optional async inserts). Validate that the addBatch/executeBatch path in TableFiller works well and tune batch sizing.
• Nullability is explicit via Nullable(T), and LowCardinality(T) wraps another type — both complicate type-name dispatch.

Scope — new dialect (own support + several new generators)

• ClickHouseSupport extends AbstractDatabaseSupport; empirical DATA_TYPE/TYPE_NAME discovery first (per feat(ext): full PostgreSQL and MySQL vendor-type support #444) — ClickHouse type names are distinctive.
• Types: UInt8/16/32/64, Int8…Int64, Float32/64, Decimal, String, FixedString(N), Date/Date32/DateTime/DateTime64, UUID, Enum8/16, Array(T), Nullable(T), LowCardinality(T), Map, Tuple, IPv4/IPv6. Reuse UUIDGenerator/InetGenerator/array generators where possible; new generators likely needed for unsigned ints, FixedString, and the wrapper types.
• forProduct: add a clickhouse branch + selection test.
• create_tables.clickhouse.sql (MergeTree tables) + fillTestTables.
• Driver: com.clickhouse:clickhouse-jdbc (test scope).

Acceptance criteria

• Decision recorded on how FK-less / non-unique semantics map to Bloviate's fill model
• ClickHouseSupport registered and selectable
• Integration test fills a representative MergeTree schema (incl. Nullable/LowCardinality/Array) cleanly
• Unsupported types throw rather than generate invalid data
• README "Database Support" table updated