fix: full_scan covers revealed range before applying stop_gap

[noahjoeris]

Fixes #2057. full_scan now always covers the revealed range before applying the stop_gap

Notes to the reviewers

Replaces #2181. That PR unified full_scan and sync into one path; per @evanlinjin's feedback we're keeping them separate and doing the minimal fix here instead

Changelog notice

Fixed: full_scan now always scans the full revealed range before applying stop_gap past last_revealed.

Checklists

All Submissions:

• I followed the contribution guidelines

New Features:

• I've added tests for the new feature
• I've added docs for the new feature

Bugfixes:

• This pull request breaks the existing API
• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[noahjoeris]

Should we combine some parameters to avoid suppressing clippy::too_many_arguments? e.g.

struct StopGapExt {
  stop_gap: usize
  last_revealed Option<u32>
}