feat(sql): extract function-name catalog, generalize uniqExact/countIf rewrite

[zzylol]

Summary

• Adds a new workspace crate, crates/sql-function-catalog (package asap-sql-function-catalog), holding the SQL aggregate-function name → canonical semantic mapping frontend-sql::lower_agg_intent used to hand-match. Design lifted from tobilg/polyglot's polyglot-sql-function-catalogs: flat per-function data (name, arity, canonical AggSemantic), with no dependency on asap-frontend-sql or DataFusion — asap-frontend-sql depends on it, not the other way around. lower_agg_intent keeps only the call-site logic that isn't a function of the name alone: the DISTINCT modifier rule, the "reducer argument must be a bare column" rule (reducer_col), φ extraction from a literal argument, and the ambient AccuracyTarget.
• Generalizes uniqExact's stub-AggregateUDF + FunctionRewrite mechanism (feat: rewrite uniqExact to COUNT(DISTINCT ...) #221) so a new ClickHouse-only builtin DataFusion doesn't know at all is a catalog data entry (name, arity, RewriteKind), not a new one-off Rust type plus a new one-off stub-UDAF function. uniqExact and a new countIf entry both go through one ClickHouseBuiltinRewrite + clickhouse_builtin_stub_udaf mechanism now.
• countIf(cond) rewrites to sum(CASE WHEN cond THEN 1 ELSE 0 END), not count(...) FILTER (WHERE cond): AggIntent::Count never consults its argument (it always means "row count"), so a plain filtered count would silently drop the filter. Summing a 0/1 indicator keeps cond observable through the existing Sum path, including the general non-column-argument materialization lower_aggregate already does (SQL: expression GROUP BY (date_trunc time bucketing), aggregates over expressions, and GROUPING SETS/ROLLUP/CUBE are rejected #110) — no new AggIntent variant or lowering path needed.

Design choices

• Crate name / shape: asap-sql-function-catalog, two flat const tables — NATIVE_FUNCTIONS (names DataFusion's planner already resolves, mapped to AggSemantic) and CLICKHOUSE_BUILTINS (ClickHouse-only names, each carrying a RewriteKind). Hand-maintained Rust consts; the module doc notes that generating them from a live ClickHouse/DataFusion introspection source is a documented follow-up (issue SQL: extract dialect builtin-function catalog into independent, generatable data (inspired by polyglot-sql-function-catalogs) #225, item 3 — explicitly flagged in the issue as needing a decision on where such tooling would run, not built here).
• AggSemantic is deliberately not asap_types::pre_asap::agg_intent::AggIntent itself — most AggIntent variants carry call-site-only state (ambient accuracy, φ from a literal arg, DISTINCT) that isn't a function of the name alone. AggSemantic is just the per-name discriminant those call sites key off.
• countIf proves the generalization: it reuses ClickHouseBuiltinRewrite/clickhouse_builtin_stub_udaf with zero new Rust types, adding only a catalog entry and one new RewriteKind::CountIfToSum match arm.

Behavior / test impact

• uniqExact's behavior is unchanged (same stub signature, same rewrite target); its existing corpus tests (bgp_analytics, from feat: rewrite uniqExact to COUNT(DISTINCT ...) #221) pass unmodified.
• countIf support moves 13 bgp_jan2024_workload corpus queries out of Category::Plan (12 now lower end to end, one hits a second, pre-existing NotImplemented gap — map/array index access) — the pinned tally in that test is updated accordingly, per its own documented ratchet convention.
• New direct unit tests in sql_lowering.rs cover countIf's derived-indicator-column shape, multiple distinct countIf calls in one aggregate, and composition with GROUP BY.

Out of scope (per the issue)

• Generating the catalog from a live ClickHouse system.functions / DataFusion UDF registry introspection (issue SQL: extract dialect builtin-function catalog into independent, generatable data (inspired by polyglot-sql-function-catalogs) #225, item 3).
• ElasticSQL having no vendored parser.
• Modeling argument/return types beyond arity.

Test plan

• cargo build --workspace --all-targets
• cargo test --workspace (all green)
• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets --all-features -- -D warnings

Closes #225