Add alloc feature to base64

Summary: This comes as part of https://github.com/project-oak/oak/blob/059354ec30611756aafb923b325fadc56185a2f2/bazel/crates/oak_crates.bzl#L47, but `base64` seems like a pretty core crate, so let's make sure CI signals pass before landing

Reviewed By: dtolnay

Differential Revision: D76646019

fbshipit-source-id: 1044e91b90607aff9db3df279b957700bef4a158

Author: CookieComputing

third-party/thrift/src/thrift/lib/rust/Cargo.toml

@@ -12,7 +12,7 @@ publish = false
 [dependencies]
 anyhow = "1.0.95"
 async-trait = "0.1.86"
-base64 = "0.22.1"
+base64 = { version = "0.22.1", features = ["alloc"] }
 bufsize = "1.0.8"
 bytes = { version = "1.9.0", features = ["serde"] }
 futures = { version = "0.3.30", features = ["async-await", "compat"] }