fix(core/txpool): avoid blocking reset completion on close #31030 (#2175)

* fix(core/txpool): coordinate reset lifecycle and shutdown signaling #28837

Improve txpool loop synchronization around background resets.

This change:
- adds an explicit termination channel to signal pool shutdown
- tracks forced-reset intent and a waiter channel inside the reset loop
- ensures reset waiters are notified on completion or on pool termination
- allows an explicit sync request path to trigger an additional reset round when needed

Scope is limited to internal txpool concurrency control in core/txpool/txpool.go, with no protocol or RPC behavior change.

* fix(core/txpool): avoid blocking reset completion on close #31030

core/txpool/txpool.go

@@ -166,7 +166,10 @@ func (p *TxPool) loop(head *types.Header, chain BlockChain) {
 					for _, subpool := range p.subpools {
 						subpool.Reset(oldHead, newHead)
 					}
-					resetDone <- newHead
+					select {
+					case resetDone <- newHead:
+					case <-p.term:
+					}
 				}(oldHead, newHead)
 
 				// If the reset operation was explicitly requested, consider it