[functional-tests] port some of the cache_check tests to Rust

Cargo.lock

@@ -53,6 +53,12 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f8aac770f1885fd7e387acedd76065302551364496e46b3dd00860b2f8359b9d"
 
+[[package]]
+name = "base64"
+version = "0.12.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3441f0f7b02788e948e47f457ca01f1d7e6d92c693bc132c22b087d3141c03ff"
+
 [[package]]
 name = "bitflags"
 version = "1.2.1"
@@ -638,6 +644,7 @@ name = "thinp"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "base64",
  "byteorder",
  "clap",
  "crc32c",