[Bug] NettyConnectionHandler.channelInactive() does not remove channel from CHANNEL_MAP causing memory leak

### Pre-check

- [x] I am sure that all the content I provide is in English.

### Search before asking

- [x] I had searched in the [issues](https://github.com/apache/dubbo/issues?q=is%3Aissue) and found no similar issues.

### Apache Dubbo Component

Java SDK (apache/dubbo)

### Dubbo Version

- Dubbo version: dubbo-dubbo.3.2.19
- Java version: 1.8
- OS: Linux
- Protocol: Triple (tri://)

### Steps to reproduce this issue

1. Configure a Dubbo consumer to call a Triple protocol service
2. The Triple service endpoint is unreachable or TLS handshake fails
3. Connection continuously fails and reconnects every second
4. Observe CHANNEL_MAP size growing unbounded

### What you expected to happen

When `channelInactive` is called, the channel should be removed from `CHANNEL_MAP` to prevent memory leak.

`NettyConnectionHandler.channelInactive()` only calls `reconnect()` but does NOT call `NettyChannel.removeChannel()`, causing channels to accumulate in `CHANNEL_MAP`.

**NettyConnectionHandler.java (BUG):**
@Override
public void channelInactive(ChannelHandlerContext ctx) throws Exception {
super.channelInactive(ctx);
final Attribute goawayAttr = ctx.channel().attr(GO_AWAY_KEY);
if (!Boolean.TRUE.equals(goawayAttr.get())) {
reconnect(ctx.channel());
}
// ❌ Missing: NettyChannel.removeChannel(ctx.channel())
}

### Anything else

_No response_

### Do you have a (mini) reproduction demo?

- [x] Yes, I have a minimal reproduction demo to help resolve this issue more effectively!

### Are you willing to submit a pull request to fix on your own?

- [x] Yes I am willing to submit a pull request on my own!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)

Start with NettyConnectionHandler.java and inspect channelInactive(), then trace NettyChannel.removeChannel() and CHANNEL_MAP. Reproduce the unreachable-endpoint or failed-TLS reconnect scenario and verify that inactive channels no longer accumulate in CHANNEL_MAP.

Written by the indexing model from the issue text.