Add structured JSON logging support

[anzheyazzz]

Description of changes:

Add structured logging support to the Ruby RIC on the Logger path, consistent with
the structured logging behavior in other Lambda managed runtimes (Python, Node.js, etc.).

When AWS_LAMBDA_LOG_FORMAT=JSON, each log output is a JSON object containing
at least four key-value pairs:

• timestamp – the time the log message was generated (ISO 8601, UTC)
• level – the log level assigned to the message (DEBUG, INFO, WARN, ERROR, FATAL)
• message – the contents of the log message
• requestId – the unique request ID for the function invocation

This PR includes the following changes:

• Add structured JSON logging support for the Ruby Logger path
• Apply formatter and log level selection based on AWS_LAMBDA_LOG_FORMAT and AWS_LAMBDA_LOG_LEVEL
• Make this behavior work consistently with and without telemetry fd, with unit test coverage

Target (OCI, Managed Runtime, both):

Both

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Example Usage:

require 'logger'

def lambda_handler(event:, context:)
    logger = Logger.new($stdout)
    logger.info("Inside the handler function")
end

Output without AWS_LAMBDA_LOG_FORMAT:

I, [2026-03-10T22:30:46.745494 #16] INFO 3244ba10-b213-4742-9cbc-fcc611f42625 -- : Inside the handler function

Output with AWS_LAMBDA_LOG_FORMAT=JSON:

{
	"timestamp":"2026-03-10T21:37:36.350555Z",
	"level":"INFO",
	"message":"Inside the handler function",
	"requestId":"d1491d62-2ed4-4d08-a1be-feea698100f7"
}