Split compact document and query execution concerns

[dv00d00]

Summary

• split CompactDocument into lifecycle, storage, query, and template-scope partials
• split QueryExecution into lifecycle/matching, token-sink, and completed-capture partials
• replace the untyped rewrite-handler union with two typed nullable fields, avoiding the auxiliary handler-pair allocation

Public API and parsing behavior are unchanged.

Validation

• CSharpier check passed for all affected files
• full Release solution build passed with 0 warnings across net10.0, net8.0, netstandard2.0, and net472
• 179,562/179,562 net10.0 tests passed
• tokenizer smoke passed for 57/57 documents (38,831,169 UTF-8 bytes)
• QQ scraper and UTF-8 DOM projection correctness checks passed