refactor: drop the liveMode IORef, thread live explicitly

[dmjio]

Summary

Removes the global liveMode :: IORef Bool (a NOINLINE / unsafePerformIO top-level ref set once in initComponent) and passes the live-reload flag as an explicit Bool argument through the runtime instead.

The flag gates key-based model recovery in initialize — outside hot reload, a keyed component must never inherit a previous (possibly unrelated) component's model just because it shares a Key. That rationale now lives on the parameter's haddock instead of the IORef's.

Changes (src/Miso/Runtime.hs)

• initialize takes a new live :: Bool parameter (after isRoot); the readIORef liveMode at the model-recovery check is replaced by the parameter.
• buildVTree gains the same parameter and threads it through both recursive child-building calls; its nested buildComp passes it to the recursive initialize for VComp / VCompStatic children — including keyed ones, where the flag actually matters.
• initialDraw gains the parameter and forwards it to both of its buildVTree calls (initial draw and the hydration-failure redraw).
• initComponent passes its existing live argument straight into initialize; the atomicWriteIORef liveMode live is deleted.
• componentListener (NATIVE / Lynx MTS) takes live as well, supplied at its registration site in initComponent, so MTS-mounted children — and their keyed descendants via buildVTree — observe the same value the IORef would have held.
• liveMode definition, NOINLINE pragma, and doc comment removed. The ref was not exported, so nothing outside Miso.Runtime is affected.
• Cosmetic: initSubs type signature reformatted to one argument per line.

Verification

• cabal build miso with the project defaults (+template-haskell +native, GHC 9.12.2) compiles cleanly — covers the NATIVE branch.
• The non-native (web / SSR) flavor, built with only +template-haskell, compiles cleanly as well.

No behavior change intended: every call site receives exactly the value the IORef would have contained at that point.