Add explicit features list to tinystr (#6040)

At this point we should always be using `dep:` to avoid confusion, and
it helps when people are looking at the features list.

utils/tinystr/Cargo.toml

@@ -41,6 +41,9 @@ criterion = { workspace = true }
 [features]
 default = ["alloc"]
 alloc = []
+zerovec = ["dep:zerovec"]
+databake = ["dep:databake"]
+serde = ["dep:serde"]
 
 [lib]
 bench = false  # This option is required for Benchmark CI