Introducing RateLimiter to Control Request Rate (Issue #4)

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Summary:

In this Pull Request, we have introduced a RateLimiter struct in the sourcify package to control the rate at which HTTP requests are sent from the client to the server. The rate limiter is based on the token bucket algorithm and provides a mechanism to prevent an HTTP client from exceeding a specified rate of requests.

Key points in the PR:

• Added a new RateLimiter struct that maintains a token bucket. Tokens are added to the bucket at a specified rate, limiting the rate at which requests can be sent. If a request is made when the bucket is empty, the request is blocked until a token is available, ensuring the rate of requests does not exceed the specified rate.
• The RateLimiter struct includes a Wait() method, which is used to control the rate of requests. Before sending a request, the client calls the Wait() method to consume a token from the bucket.
• Integrated the RateLimiter into the Client struct. The Client now includes a RateLimiter that is used to control the rate of requests when the doRequestWithRetry method is called.
• Updated existing unit tests to include rate limiting and added new unit tests specifically for the RateLimiter.

By introducing the RateLimiter, we aim to improve the reliability and robustness of the client by preventing it from overwhelming the server with requests and being rate-limited or banned. This also promotes more efficient use of server resources.

WARN: Prior this PR is merged, #6 needs to be resolved first.

This PR closes #4