Add plain text and coloured logging to the Client

Logs websocket events (connect, message, error and close events)

docs/common-use-cases/logging-and-debugging.md

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+# Logging and debugging
+
+The `Nostr::Client` class provides built-in logging functionality to help you debug and monitor client interactions with
+relays. By default, the client uses the `ColorLogger`, which logs events in color. However, you can customize the
+logging behavior or disable it entirely.
+
+## Disabling logging
+
+To instantiate a client without any logging, simply pass `logger: nil` when creating the client instance:
+
+```ruby
+client = Nostr::Client.new(logger: nil)
+```
+
+This will disable all logging for the client.
+
+## Formatting the logging
+
+The `Nostr::Client::Logger` class is the base class for logging functionality. It defines the following methods for
+logging different events:
+
+- `on_connect(relay)`: Logs when the client connects to a relay.
+- `on_message(message)`: Logs a message received from the relay.
+- `on_send(message)`: Logs a message sent to the relay.
+- `on_error(message)`: Logs an error message.
+- `on_close(code, reason)`: Logs when the connection with a relay is closed.
+
+You can create your own logger by subclassing `Nostr::Client::Logger` and overriding these methods to customize the
+logging format.
+
+The `Nostr::Client::ColorLogger` is a built-in logger that logs events in color. It uses ANSI escape codes to add color
+to the log output. Here's an example of how the ColorLogger formats the log messages:
+
+- Connection: `"\u001b[32m\u001b[1mConnected to the relay\u001b[22m #{relay.name} (#{relay.url})\u001b[0m"`
+- Message received: `"\u001b[32m\u001b[1m◄-\u001b[0m #{message}"`
+- Message sent: `"\u001b[32m\u001b[1m-►\u001b[0m #{message}"`
+- Error: `"\u001b[31m\u001b[1mError: \u001b[22m#{message}\u001b[0m"`
+- Connection closed: `"\u001b[31m\u001b[1mConnection closed: \u001b[22m#{reason} (##{code})\u001b[0m"`
+
+## Plain text logging
+
+If you prefer plain text logging without colors, you can use the `Nostr::Client::PlainLogger`. This logger formats the
+log messages in a simple, readable format without any ANSI escape codes.
+
+To use the `PlainLogger`, pass it as the `logger` option when creating the client instance:
+
+```ruby
+client = Nostr::Client.new(logger: Nostr::Client::PlainLogger.new)
+```
+
+The `PlainLogger` formats the log messages as follows:
+
+- Connection: `"Connected to the relay #{relay.name} (#{relay.url})"`
+- Message received: `"◄- #{message}"`
+- Message sent: `"-► #{message}"`
+- Error: `"Error: #{message}"`
+- Connection closed: `"Connection closed: #{reason} (##{code})"`
+
+By using the appropriate logger or creating your own custom logger, you can effectively debug and monitor your Nostr
+client's interactions with relays.