jid: Make the crate no_std

Only std::error::Error is missing in this mode, but that’s only waiting
for its stabilisation, see this issue:
https://github.com/rust-lang/rust/issues/103765

jid/Cargo.toml

@@ -32,4 +32,6 @@ serde_test = "1"
 jid = { path = ".", features = [ "serde" ] }
 
 [features]
+default = ["std"]
+std = []
 quote = ["dep:quote", "dep:proc-macro2"]