Reduce time spent logging EventLoop description in HTTP1ClientChannelHandler (#772)

### Motivation:

A performance test executing 100,000 sequential requests against a
simple
[`NIOHTTP1Server`](https://github.com/apple/swift-nio/blob/main/Sources/NIOHTTP1Server/README.md)
revealed that 7% of total run time is spent in the setter of the
`request` property in `HTTP1ClientChannelHandler` (GitHub Issue #754).

The poor performance comes from [processing the string interpolation
`"\(self.eventLoop)"`](https://github.com/swift-server/async-http-client/blob/6df8e1c17e68f0f93de2443b8c8cafca9ddcc89a/Sources/AsyncHTTPClient/ConnectionPool/HTTP1/HTTP1ClientChannelHandler.swift#L39C17-L39C75)
which under the hood calls a computed property.

This problem can entirely be avoided by storing `eventLoop.description`
when initializing `HTTP1ClientChannelHandler`, and using that stored
value in `request`'s setter, rather than computing the property each
time.

### Modifications:

- Created a new property `let eventLoopDescription:
Logger.MetadataValue` in `HTTP1ClientChannelHandler` that stores the
description of the `eventLoop` argument that is passed into the
initializer.
- Replaced the string interpolation `"\(self.eventLoop)"` in `request`'s
setter with `self.eventLoopDescription`.

### Result:

`HTTP1ClientChannelHandler.eventLoop`'s `description` property is cached
upon initialization rather than being computed each time in the
`request` property's setter.

---------

Co-authored-by: Cory Benfield <lukasa@apple.com>

Author: aryan-25

Sources/AsyncHTTPClient/ConnectionPool/HTTP1/HTTP1ClientChannelHandler.swift

@@ -36,7 +36,7 @@ final class HTTP1ClientChannelHandler: ChannelDuplexHandler {
             if let newRequest = self.request {
                 var requestLogger = newRequest.logger
                 requestLogger[metadataKey: "ahc-connection-id"] = self.connectionIdLoggerMetadata
-                requestLogger[metadataKey: "ahc-el"] = "\(self.eventLoop)"
+                requestLogger[metadataKey: "ahc-el"] = self.eventLoopDescription
                 self.logger = requestLogger
 
                 if let idleReadTimeout = newRequest.requestOptions.idleReadTimeout {
@@ -72,11 +72,13 @@ final class HTTP1ClientChannelHandler: ChannelDuplexHandler {
     private let backgroundLogger: Logger
     private var logger: Logger
     private let eventLoop: EventLoop
+    private let eventLoopDescription: Logger.MetadataValue
     private let connectionIdLoggerMetadata: Logger.MetadataValue
 
     var onConnectionIdle: () -> Void = {}
     init(eventLoop: EventLoop, backgroundLogger: Logger, connectionIdLoggerMetadata: Logger.MetadataValue) {
         self.eventLoop = eventLoop
+        self.eventLoopDescription = "\(eventLoop.description)"
         self.backgroundLogger = backgroundLogger
         self.logger = backgroundLogger
         self.connectionIdLoggerMetadata = connectionIdLoggerMetadata