Improve the performance of ConnState.String()

[ksw2000]

Decrease the ConnState.String() runtime by 95%.

We can replace the map with []string like the code in

fasthttp/status.go

Lines 85 to 151 in 65e989e

	statusMessages = []string{
	StatusContinue: "Continue",
	StatusSwitchingProtocols: "Switching Protocols",
	StatusProcessing: "Processing",
	StatusEarlyHints: "Early Hints",
	StatusOK: "OK",
	StatusCreated: "Created",
	StatusAccepted: "Accepted",
	StatusNonAuthoritativeInfo: "Non-Authoritative Information",
	StatusNoContent: "No Content",
	StatusResetContent: "Reset Content",
	StatusPartialContent: "Partial Content",
	StatusMultiStatus: "Multi-Status",
	StatusAlreadyReported: "Already Reported",
	StatusIMUsed: "IM Used",
	StatusMultipleChoices: "Multiple Choices",
	StatusMovedPermanently: "Moved Permanently",
	StatusFound: "Found",
	StatusSeeOther: "See Other",
	StatusNotModified: "Not Modified",
	StatusUseProxy: "Use Proxy",
	StatusTemporaryRedirect: "Temporary Redirect",
	StatusPermanentRedirect: "Permanent Redirect",
	StatusBadRequest: "Bad Request",
	StatusUnauthorized: "Unauthorized",
	StatusPaymentRequired: "Payment Required",
	StatusForbidden: "Forbidden",
	StatusNotFound: "Not Found",
	StatusMethodNotAllowed: "Method Not Allowed",
	StatusNotAcceptable: "Not Acceptable",
	StatusProxyAuthRequired: "Proxy Authentication Required",
	StatusRequestTimeout: "Request Timeout",
	StatusConflict: "Conflict",
	StatusGone: "Gone",
	StatusLengthRequired: "Length Required",
	StatusPreconditionFailed: "Precondition Failed",
	StatusRequestEntityTooLarge: "Request Entity Too Large",
	StatusRequestURITooLong: "Request URI Too Long",
	StatusUnsupportedMediaType: "Unsupported Media Type",
	StatusRequestedRangeNotSatisfiable: "Requested Range Not Satisfiable",
	StatusExpectationFailed: "Expectation Failed",
	StatusTeapot: "I'm a teapot",
	StatusMisdirectedRequest: "Misdirected Request",
	StatusUnprocessableEntity: "Unprocessable Entity",
	StatusLocked: "Locked",
	StatusFailedDependency: "Failed Dependency",
	StatusUpgradeRequired: "Upgrade Required",
	StatusPreconditionRequired: "Precondition Required",
	StatusTooManyRequests: "Too Many Requests",
	StatusRequestHeaderFieldsTooLarge: "Request Header Fields Too Large",
	StatusUnavailableForLegalReasons: "Unavailable For Legal Reasons",
	StatusInternalServerError: "Internal Server Error",
	StatusNotImplemented: "Not Implemented",
	StatusBadGateway: "Bad Gateway",
	StatusServiceUnavailable: "Service Unavailable",
	StatusGatewayTimeout: "Gateway Timeout",
	StatusHTTPVersionNotSupported: "HTTP Version Not Supported",
	StatusVariantAlsoNegotiates: "Variant Also Negotiates",
	StatusInsufficientStorage: "Insufficient Storage",
	StatusLoopDetected: "Loop Detected",
	StatusNotExtended: "Not Extended",
	StatusNetworkAuthenticationRequired: "Network Authentication Required",
	}

func BenchmarkStatusToString(b *testing.B) {
	for i := 0; i < b.N; i++ {
		StateNew.String()
		StateActive.String()
		StateIdle.String()
		StateHijacked.String()
		StateClosed.String()
	}
}

goos: linux
goarch: amd64
pkg: github.com/valyala/fasthttp
cpu: Intel(R) Core(TM) i7-4790 CPU @ 3.60GHz
                 │    old.txt    │           new.txt            │
                 │    sec/op     │    sec/op     vs base        │
StatusToString-8   18.9250n ± 0%   0.8873n ± 1%  -95.31% (n=50)

                 │  old.txt   │            new.txt             │
                 │    B/op    │    B/op     vs base            │
StatusToString-8   0.000 ± 0%   0.000 ± 0%  ~ (p=1.000 n=50) ¹
¹ all samples are equal

                 │  old.txt   │            new.txt             │
                 │ allocs/op  │ allocs/op   vs base            │
StatusToString-8   0.000 ± 0%   0.000 ± 0%  ~ (p=1.000 n=50) ¹
¹ all samples are equal

[erikdubbelboer]

Thanks!