Wire NewlineFramer and CRI parser to StructuralIndex bitmasks #335

Summary

NewlineFramer currently scans bytes in a loop. CRI field extraction parses spaces per-line. Both can consume bitmasks from ProcessedBlock instead — the SIMD pass already detected newlines and spaces.

Changes

NewlineFramer

• Accept ProcessedBlock.newline bitmask instead of scanning input[i] == b'\n'
• Extract line ranges via trailing_zeros + clear-lowest-bit
• Line ranges are a byproduct of the SIMD pass — zero additional work

CRI field extraction

• Accept ProcessedBlock.space (masked by !in_string) bitmask
• Find space positions via trailing_zeros instead of find_byte(line, b' ', from)
• CRI timestamp/stream/flags boundaries become bitmask lookups

Dependencies

• Migrate scanner from ChunkIndex to StreamingClassifier #332 (scanner migration) or can be done independently
• structural.rs prototype (done)