refactor(r8): Replace no-line resolution with base entry grouping (#85)

## Summary
- Rewrites no-line frame resolution in both mapper and cache paths to
properly handle different base entry types (0:0 range vs bare method vs
single-line mappings)
- Extracts resolution logic into `resolve_no_line_frames` /
`resolve_base_entries` helper functions that use `Option` field presence
(`startline.is_some()`, `original_startline.is_some()`) instead of the
removed
  boolean flags
- Simplifies `resolve_base_entries` from a two-pass Vec collection to a
single-pass approach
- Adds `pending_frames` buffer to cache `RemappedFrameIter` for
multi-frame base entry resolution
  - Removes unused `resolve_no_line_output_line` from utils

  ## Test plan
  - [x] All existing tests pass (50 unit + all integration tests)
- [x] 3 pre-existing failures in r8-line-number-handling remain
(targeted by subsequent PRs)
  - [x] No new warnings

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: romtsn