Add unit tests for asap-common library crates

[milindsrivastava1997]

Problem

All library crates under asap-common/ have zero #[test] functions. cargo test --workspace runs 0 tests for:

• sketch-core
• promql_utilities
• sql_utilities
• sketch_db_common
• elastic_dsl_utilities
• datafusion_summary_library

Some binary test runners exist under asap-common/tests/ but they aren't cargo test-integrated.

Scope

Crate	Priority	Notes
sketch-core	High	Algorithmic (KLL, CountMin, HLL) — test accuracy bounds, merges, edge cases
promql_utilities	High	AST pattern matching — can partially migrate existing binary test runners
sketch_db_common	Medium	capability_matching.rs (792 LOC) is logic-heavy; config parsing deserves coverage
sql_utilities	Medium	SQL pattern matching
elastic_dsl_utilities	Low	Elasticsearch DSL parsing
datafusion_summary_library	Low	Custom DataFusion physical operators — may need integration-style tests

Additional cleanup

Consider migrating the binary test runners (rust_pattern_matching, compare_matched_tokens, compare_patterns) into #[test] functions within promql_utilities so they run with cargo test.