Added checked_sqrt to the FixedPointNumber trait (paritytech#8238)

Adds `checked_sqrt` function to `FixedPointNumber` and renames `const fn
try_sqrt` in the `implement_fixed` macro to `const fn checked_sqrt`.

CLOSES: paritytech#8214 

## Integration

Any projects that use the **const** function `try_sqrt` from `FixedI64`,
`FixedU64`, `FixedI128`, `FixedU128` should now use `checked_sqrt`.

## Review Notes

- renamed the const `try_sqrt` with `checked_sqrt`
- updated tests for new name
- added `checked_sqrt` to impl of `FixedPointNumber`

We keep both the const version along with adding the non-const version
of `checked_sqrt` so that we can now access `checked_sqrt` from
associated types that implement `FixedPointNumber` without breaking all
of the uses of `sqrt` that rely on it being const.

---------

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: Bastian Köcher <git@kchr.de>

Author: 3 people

prdoc/pr_8238.prdoc

@@ -0,0 +1,12 @@
+title: Add `checked_sqrt` to the `FixedPointNumber` trait
+
+doc:
+- audience: Runtime Dev
+  description: |-
+    Adds the function `checked_sqrt` to the `FixedPointNumber` trait, and deprecates `const fn try_sqrt` inside
+    of the `implement_fixed` macro in favor of a `const fn checked_sqrt` which does the same thing. This affects 
+    [`FixedI64`, `FixedU64`, `FixedI128`, `FixedU128`].
+
+crates:
+- name: sp-arithmetic
+  bump: major

substrate/primitives/arithmetic/src/fixed_point.rs

@@ -140,6 +140,9 @@ pub trait FixedPointNumber:
 	/// Consumes `self` and returns the inner raw value.
 	fn into_inner(self) -> Self::Inner;
 
+	/// Compute the square root. If it overflows or is negative, then `None` is returned.
+	fn checked_sqrt(self) -> Option<Self>;
+
 	/// Creates self from an integer number `int`.
 	///
 	/// Returns `Self::max` or `Self::min` if `int` exceeds accuracy.
@@ -443,6 +446,10 @@ macro_rules! implement_fixed {
 			fn into_inner(self) -> Self::Inner {
 				self.0
 			}
+
+			fn checked_sqrt(self) -> Option<Self> {
+				self.checked_sqrt()
+			}
 		}
 
 		impl $name {
@@ -551,15 +558,21 @@ macro_rules! implement_fixed {
 			/// WARNING: This is a `const` function designed for convenient use at build time and
 			/// will panic on overflow. Ensure that any inputs are sensible.
 			pub const fn sqrt(self) -> Self {
-				match self.try_sqrt() {
+				match self.checked_sqrt() {
 					Some(v) => v,
 					None => panic!("sqrt overflow or negative input"),
 				}
 			}
 
-			/// Compute the square root, rounding as desired. If it overflows or is negative, then
-			/// `None` is returned.
+			#[deprecated(
+				note = "`try_sqrt` will be removed after October 2025. Use `checked_sqrt` instead."
+			)]
 			pub const fn try_sqrt(self) -> Option<Self> {
+				self.checked_sqrt()
+			}
+
+			/// Compute the square root. If it overflows or is negative, then `None` is returned.
+			pub const fn checked_sqrt(self) -> Option<Self> {
 				if self.0 == 0 {
 					return Some(Self(0))
 				}
@@ -1211,9 +1224,9 @@ macro_rules! implement_fixed {
 			fn op_sqrt_works() {
 				for i in 1..1_000i64 {
 					let x = $name::saturating_from_rational(i, 1_000i64);
-					assert_eq!((x * x).try_sqrt(), Some(x));
+					assert_eq!((x * x).checked_sqrt(), Some(x));
 					let x = $name::saturating_from_rational(i, 1i64);
-					assert_eq!((x * x).try_sqrt(), Some(x));
+					assert_eq!((x * x).checked_sqrt(), Some(x));
 				}
 			}