Bound Unsigned when signed is not supported. (#6367)

* bound unsigned when necessary

* convert more type to AtLeast32BitUnsigned

* Update primitives/arithmetic/src/traits.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* doc refactor

* line reorganize

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

substrate/frame/support/src/traits.rs

@@ -25,7 +25,7 @@ use sp_core::u32_trait::Value as U32;
 use sp_runtime::{
 	RuntimeDebug, ConsensusEngineId, DispatchResult, DispatchError, traits::{
 		MaybeSerializeDeserialize, AtLeast32Bit, Saturating, TrailingZeroInput, Bounded, Zero,
-		BadOrigin
+		BadOrigin, AtLeast32BitUnsigned
 	},
 };
 use crate::dispatch::Parameter;
@@ -788,7 +788,7 @@ pub enum SignedImbalance<B, P: Imbalance<B>>{
 impl<
 	P: Imbalance<B, Opposite=N>,
 	N: Imbalance<B, Opposite=P>,
-	B: AtLeast32Bit + FullCodec + Copy + MaybeSerializeDeserialize + Debug + Default,
+	B: AtLeast32BitUnsigned + FullCodec + Copy + MaybeSerializeDeserialize + Debug + Default,
 > SignedImbalance<B, P> {
 	pub fn zero() -> Self {
 		SignedImbalance::Positive(P::zero())
@@ -851,7 +851,8 @@ impl<
 /// Abstraction over a fungible assets system.
 pub trait Currency<AccountId> {
 	/// The balance of an account.
-	type Balance: AtLeast32Bit + FullCodec + Copy + MaybeSerializeDeserialize + Debug + Default;
+	type Balance: AtLeast32BitUnsigned + FullCodec + Copy + MaybeSerializeDeserialize + Debug +
+		Default;
 
 	/// The opaque token type for an imbalance. This is returned by unbalanced operations
 	/// and must be dealt with. It may be dropped but cannot be cloned.