[feature-request] sticky and negated file filters #166

Is your feature request related to a problem?
When reviewing a large diff I often want to focus on a subset of files (e.g. only ui/ files, or everything except tests). The t search only jumps to a single file, then the tree goes back to showing everything, and there's no way to exclude files from the search.

Describe the solution you'd like

1. A way to keep the file tree filtered to the search matches while navigating (n/p, j/k, directory diffs), cleared with esc.
2. Negated terms in the file search, e.g. !test, combinable with other terms: ui !test.

Additional context
I have draft PRs for both: #164 (sticky filter) and #165 (negation).