plugin/fragment: clean up nested fragments when removing a block

[rameel]

Call destroyTree before removing block contents so nested fragments,
effects and event listeners are cleaned up even when Alpine's mutation
observer is paused.

Fixes #63

[github-actions]

📦 Bundle size comparison

Name	Size	Gzip	Brotli	Δ
alpinegear-bound.esm.min.js	3.91 KiB	1.80 KiB	1.56 KiB
alpinegear-bound.min.js	3.95 KiB	1.82 KiB	1.58 KiB
alpinegear-destroy.esm.min.js	128 B	123 B	91 B
alpinegear-destroy.min.js	191 B	167 B	123 B
alpinegear-dialog.esm.min.js	1.75 KiB	951 B	811 B
alpinegear-dialog.min.js	1.79 KiB	967 B	822 B
alpinegear-format.esm.min.js	1.18 KiB	642 B	556 B
alpinegear-format.min.js	1.24 KiB	677 B	584 B
alpinegear-fragment.esm.min.js	1.02 KiB (+62 B)	539 B (+18 B)	462 B (+5 B)	🔴
alpinegear-fragment.min.js	1.08 KiB (+62 B)	571 B (+19 B)	488 B (+4 B)	🔴
alpinegear-hotkey.esm.min.js	1.97 KiB	1.08 KiB	964 B
alpinegear-hotkey.min.js	2.03 KiB	1.10 KiB	996 B
alpinegear-main.esm.min.js	7.22 KiB (+118 B)	2.93 KiB (+27 B)	2.58 KiB (+23 B)	🔴
alpinegear-main.min.js	7.18 KiB (+118 B)	2.88 KiB (+22 B)	2.54 KiB (+23 B)	🔴
alpinegear-match.esm.min.js	1.49 KiB (+62 B)	766 B (+18 B)	670 B (+10 B)	🔴
alpinegear-match.min.js	1.55 KiB (+62 B)	797 B (+19 B)	690 B (+9 B)	🔴
alpinegear-router.esm.min.js	9.40 KiB	4.03 KiB	3.59 KiB
alpinegear-router.min.js	9.42 KiB	4.04 KiB	3.60 KiB
alpinegear-safehtml.esm.min.js	28.67 KiB	10.74 KiB	9.58 KiB
alpinegear-safehtml.min.js	28.73 KiB	10.78 KiB	9.63 KiB
alpinegear-template.esm.min.js	421 B	294 B	219 B
alpinegear-template.min.js	483 B	326 B	246 B
alpinegear-typegrab.esm.min.js	471 B	333 B	277 B
alpinegear-typegrab.min.js	509 B	348 B	294 B
alpinegear-when.esm.min.js	1.21 KiB (+62 B)	645 B (+20 B)	556 B (+8 B)	🔴
alpinegear-when.min.js	1.28 KiB (+62 B)	675 B (+18 B)	580 B (+10 B)	🔴