draft: client find methods into search module.

[neo451]

• find_tag should satisfy all the constraints mentioned in fix: avoid tag false positives #206 and use cache.
• find_backlinks is identical to client.find_backlinks_async.
• find_links should find links in current buffer or any note object.

PR Checklist

• The PR contains a description of the changes
• I read the [CONTRIBUTING.md] file
• The CHANGELOG.md is updated
• The changes are documented in the README.md file
• The code complies with make chores (for style, lint, types, and tests)