feat(svg): shrink and accelerate animated output

[balcsida]

Summary

• reduce animated SVG size and rendering work with buffered streaming, compact timelines, merged backgrounds, and reuse of repeated rows and cell spans
• add opt-in frame/band/auto layouts, CSS/SMIL animation, animated href switching, and maximum-FPS sampling while keeping existing defaults lossless
• preserve cursor-only frames, underlined whitespace, timeline boundaries, and legacy idle-cap floating-point behavior
• add renderer benchmarks, SVG metrics, a layout comparison tool, and drift checks
• regenerate every example with its smallest measured profile, totaling 656,581 bytes

Impact

Default exports retain their existing lossless behavior. Experimental modes allow callers to trade compatibility or temporal resolution for smaller output; the checked-in 30 FPS examples intentionally use temporal sampling.

Validation

• go test -race ./...
• go vet ./...
• go build ./cmd/termsvg
• xmllint --noout examples/*.svg
• byte-for-byte regeneration of all six example SVGs
• git diff --check

Demo in Safari 26.6

original.mov

optimised.mov

[MrMarble]

Wow quite the contribution! Thanks!
I'll review the changes

[balcsida]

I put it back to draft as there is a few things that I would like to try out before giving up to squeeze more performance and/or smaller output filesizes out

[balcsida]

Thanks for the patience, @MrMarble, could you please check this now?

[MrMarble]

Thanks for the patience, @MrMarble, could you please check this now?

Currently spending time with the family, won't have a computer until next week, but it looks promising!
Thanks a lot!