chore: refactor searcher operations out of master side searchers

[azhou-determined]

Ticket

Description

refactor of master-side searchers:

• remove usage of searcher operations
• remove usage of max_length master-side
• rewrite of preview-search
• renames trial -> run in new code
• rewrite of progress calculation

TODO:

• code cleanup / add comments
• rewrite/add tests
• update docs

Test Plan

Checklist

• [ ] Changes have been manually QA'd
• [ ] New features have been approved by the corresponding PM
• [ ] User-facing API changes have the "User-facing API Change" label
• [ ] Release notes have been added as a separate file under docs/release-notes/ See Release Note for details.
• [ ] Licenses have been included for new code which was copied and/or modified from any external code