feat: reduce MSRV as much as possible

Author: pjox

Cargo.toml

@@ -1,11 +1,11 @@
 [package]
 name = "cc-downloader"
 version = "0.6.1"
-edition = "2024"
+edition = "2021"
 authors = ["Pedro Ortiz Suarez <pedro@commoncrawl.org>"]
 description = "A polite and user-friendly downloader for Common Crawl data."
 license = "MIT OR Apache-2.0"
-rust-version = "1.85"
+rust-version = "1.81"
 readme = "README.md"
 homepage = "https://commoncrawl.org"
 repository = "https://github.com/commoncrawl/cc-downloader"