aiosend: Deserialization of request body before signature verification (Pre-auth DoS) in webhook handler

aiosend is a synchronous and asynchronous Crypto Pay API client. Pror to version 3.0.7, `WebhookHandler.feed_update()` deserializes the entire request body before verifying the HMAC signature. This allows an unauthenticated attacker to force expensive parsing of arbitrary JSON payloads that will ultimately be rejected, leading to unnecessary CPU and memory consumption. Version 3.0.7 fixes the issue. Some workarounds are available. Restrict request body size at the reverse proxy or web framework, rate-limit webhook endpoints, and/or reject oversized requests before JSON parsing.