fix stale hx-* handlers on re-process

[scriptogre]

Fixes stale hx-on/hx-trigger handlers after morph or re-process.

Previously:

btn.setAttribute('hx-on:click', 'doV2()')
htmx.process(btn)
btn.click() // fired doV1 AND doV2

Now only the current handler fires. Cleanup is scoped to elements whose wiring attrs (hx-trigger, hx-boost, hx-on*) actually changed. hx-vals changes, hx-trigger with once modifiers, and child elements are unaffected.

Adds 12 tests. All of #3830 / #3834's tests pass.

Related: #3830, #3834