[randlee]

Fixes final FUZZ-171 scanner regressions.

• recognizes + whitespace-control markers and quoted closing delimiters
• tracks set, with, macro, call, filtered-loop and recursive-loop locals
• recognizes a double-brace expression that starts with a dictionary literal

Verification:

• cargo test -p sc-composer
• cargo test -p sc-compose
• cargo clippy -p sc-composer -p sc-compose --all-targets --all-features -- -D warnings
• supplied final-fuzz scanner probe