Improve variable terminal width support

[Rohitth007]

What does this PR do? This PR improves terminal width readability and support for both small and wide terminals.

Partial fix for #1005

topic link

Tested?

• [x] Manually
• [x] Existing tests (adapted, if necessary)
• [x] New tests added (for any new behavior)
• [x] Passed linting & tests (each commit)

Commit flow

Commit 1: ui: Make ZT go to into autohide mode if terminal is small. Commit 2: ui: Fix center panel width and add padding for wide terminals.

Interactions

Related PR #388

Visual changes To be added (many cases)

[Rohitth007]

@neiljp I think having assert statements in else is unnecessary and disturbs the way it reads. Do we need it?

[Rohitth007]

Re preserving focus, yes it is resolved. Re vertical border, I'm don't think it can be changed dynamically, it has to be set once but that means horizontal space would be lost. Anyway, if we color the side panels differently (division based on color) then it should not look odd?

[zulipbot]

Heads up @Rohitth007, we just merged some commits that conflict with the changes your made in this pull request! You can review this repository's recent commits to see where the conflicts occur. Please rebase your feature branch against the upstream/main branch and resolve your pull request's merge conflicts accordingly.