HTTP2 go away at the protocol level lets the request hang

We currently ignore the error code of the go away. I think if it is a protocol error we will never receive any further HTTP2Frame on the connection or any stream and need manually cancel all active streams. Maybe this is better handled at the nio http2 level but I'm not sure yet.

Reproducer:

    func testGoAwayFromServerDoesntHangRequest() throws {
        //try XCTSkipIf(true, "this currently hangs")
        let bin = HTTPBin(.http2())
        defer { XCTAssertNoThrow(try bin.shutdown()) }
        
        let loggerFactor = StreamLogHandler.standardOutput(label:)
        var bgLogger = Logger(label: "BG", factory: loggerFactor)
        bgLogger.logLevel = .trace
        
        let client = HTTPClient(
            eventLoopGroupProvider: .createNew,
            configuration: .init(certificateVerification: .none),
            backgroundActivityLogger: bgLogger
        )
        
        defer { XCTAssertNoThrow(try client.syncShutdown()) }
        
        var request = try HTTPClient.Request(url: bin.baseURL, method: .POST)
        // add ~64 KB header
        let headerValue = String(repeating: "0", count: 1024)
        for headerID in 0..<64 {
            request.headers.replaceOrAdd(name: "larg-header-\(headerID)", value: headerValue)
        }

        // non empty body is important to trigger this bug as we otherwise finish the request in a single flush
        request.body = .byteBuffer(ByteBuffer(bytes: [0]))

        var rqLogger = Logger(label: "RQ", factory: loggerFactor)
        rqLogger.logLevel = .trace
        
        XCTAssertThrows(try client.execute(request: request, deadline: .distantFuture, logger: rqLogger).wait())
    }

Start with Sources/AsyncHTTPClient/ConnectionPool/HTTP2/HTTP2IdleHandler.swift, especially the handling of the HTTP/2 GOAWAY error code. Run the reproducer testGoAwayFromServerDoesntHangRequest, which uses a non-empty request body and a distant-future deadline. Done means the request no longer hangs and the test observes the expected thrown error.