fix(deps): update rust crate flagsmith-flag-engine to 0.6

Author: renovate[bot]

crates/flagsmith/Cargo.toml

@@ -39,7 +39,7 @@ url = "2.5"
 reqwest = { version = "0.11", default-features = false }
 
 # Flagsmith flag engine types (must match flagsmith version)
-flagsmith-flag-engine = "0.5"
+flagsmith-flag-engine = "0.6"
 
 [dev-dependencies]
 # Testing