refactor(timeseriesql): shared scan module and split to_clickhouse

[austin-barrington]

Summary

• Add shared scan.rs for quote/regex/paren masking used by both the SELECT clause scanner and DDL lexer, eliminating regex/division drift between parsing paths.
• Split monolithic to_clickhouse.rs into focused submodules (select, conditions, aggregates, materialized_view, time_bounds, etc.) with public API preserved via re-exports.
• Fix conservative OR-aware extract_time_bounds for WITH FILL anchoring: envelope min/max only when every OR disjunct defines that side; add regression tests for partial-bound OR and split_statements paren/semicolon behavior.

Test plan

• cargo test --lib timeseriesql:: (210 passed)
• cargo test --test compat (215 passed)
• cargo clippy --lib -p hyperbytedb -- -D warnings

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Stale comment

Left a non-blocking comment: Cursor Bugbot completed with 1 unresolved finding (quoted BEGIN/END masking in statement splitting), so this is not approved. Human review is needed; no reviewer assignment tool is available in this run.

  

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Stale comment

Left a non-blocking comment: Cursor Bugbot previously reported 1 unresolved finding (quoted BEGIN/END masking in statement splitting), and no current approving review exists, so this is not approved. Human review is needed; reviewer assignment is unavailable in this run.

  

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Stale comment

Left a non-blocking comment: Cursor Bugbot’s prior finding remains unresolved (quoted BEGIN/END masking in statement splitting), and there is no current approving review, so this is not approved. Human review is needed; reviewer assignment is unavailable in this run.

  

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Approved: Cursor Bugbot was not present on this run, and its prior finding is resolved with no open automated findings requiring human review. No reviewers were assigned (assignment tool unavailable).

  

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