chore: Add clippy lints (#529)

Lints are added (deny) at crate level.

In each offending file, the failing lints are explicitly allowed.
Each file will be fixed in subsequent PRs.

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

src/languages/rego/compiler/function_calls.rs

@@ -1,5 +1,13 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
+#![allow(
+    clippy::arithmetic_side_effects,
+    clippy::indexing_slicing,
+    clippy::unseparated_literal_suffix,
+    clippy::as_conversions,
+    clippy::unused_trait_names,
+    clippy::pattern_type_mismatch
+)]
 
 use super::{Compiler, CompilerError, Register, Result};
 use crate::ast::ExprRef;