perf: compress kitty forwarding when png is supported

[samehkhamis]

Herdr decodes pane images into raw pixels before forwarding them to the host terminal. For continuously updated graphics, the resulting output traffic can delay visible responses to input.

This change queries the host terminal's Kitty PNG support during Unix client startup. A successful response enables lossless PNG forwarding for RGB/RGBA images through the existing encoder dependency. Rejection, silence, or an encoding error preserves raw forwarding. The asynchronous query uses the existing input framing and does not block startup.

The minimum render interval also changes from 16 ms to 8 ms to permit presentation above 60 FPS. This affects all actively redrawing panes and may increase CPU usage.

Validation:

• just ci passed: formatting, Clippy, 3,354 Rust tests, 107 Python tests, and 29 integration tests. XDG_RUNTIME_DIR was unset because it pointed to a nonexistent directory in the local environment.
• Real client/server tests covered successful, rejected, unanswered, and delayed PNG replies, including mouse/reset interaction.
• Four rendering benchmarks passed, including 1- and 15-pane configurations.
• Continuous 800×600 image updates at a 120 FPS target delivered approximately 77 complete images per second to the outer terminal stream. This measures data delivery, not monitor refresh.

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[kangal-bot]

Hi @samehkhamis, thanks for your interest in contributing.

Herdr does not accept unsolicited implementation pull requests from contributors who are not listed in .github/APPROVED_CONTRIBUTORS.

The pull request author is not an approved contributor.

If you encountered a reproducible bug, report the observed behavior through the bug issue template. A report does not reserve the work or authorize a pull request; accepted fixes are normally implemented by Herdr’s maintainer-controlled agents.

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