Skip post-warp-sync wait in parachain bootstrap

[lrubasze]

Problem

After a relay-chain warp sync, the runtime_service places the warp-synced block directly as the outer finalized_block — it never enters the inner async_tree, so subscribers never receive Block/Finalized notifications for it. fetch_parachain_head_from_relay waits for the next Notification::Finalized, which only fires when the relay finalizes the block after the warp-synced one (~6–12 s).

Fix

Reshape the warp-sync MustSubscribe path so the warp-synced block flows through the normal OutputUpdate::Block → OutputUpdate::Finalized sequence:

• Previous finalized block (pre_warp_finalized) becomes the tree's initial finalized state — a tree-level predecessor only, not the real chain parent.
• Warp-synced block is inserted as a non-finalized child with its runtime pre-completed (no actual download), then input_finalize'd.
• Subscribers receive pre_warp_finalized as initial finalized, then Block(warp_synced) + Finalized(warp_synced) on the channel back-to-back.

pre_warp_finalized is pruned the moment warp-synced is finalized; its placeholder runtime is Err(CodeNotFound).

This PR replaces #3210

[lrubasze]

Benchmark results

Paseo + Asset Hub Paseo, time-to-finalized, n=10 iterations.

Mode	Baseline main branch f4f2b69e (median / p95 / max)	PR f361eab2 (median / p95 / max)	Speedup (median / p95)
Cold	11.4s / 56.4s / 59.1s	5.5s / 9.8s / 12.3s	2.1× / 5.8×
Warm	17.8s / 91.0s / 92.9s	4.1s / 7.9s / 9.0s	4.3× / 11.5×

Highlights:

• Warm variance collapses: σ 30.0s → 1.7s.
• Cold variance: σ 18.2s → 2.2s; worst run 12.3s vs baseline 59.1s.
• Baseline warm had 1/10 run fail to finalize; PR has 10/10.