perf: inline a few trivial Array functions

src/Init/Data/Array/Basic.lean

@@ -283,7 +283,7 @@ Examples:
  * `#[1, 2].isEmpty = false`
  * `#[()].isEmpty = false`
 -/
-@[expose]
+@[expose, inline]
 def isEmpty (xs : Array α) : Bool :=
   xs.size = 0
 
@@ -377,6 +377,7 @@ Returns the last element of an array, or panics if the array is empty.
 Safer alternatives include `Array.back`, which requires a proof the array is non-empty, and
 `Array.back?`, which returns an `Option`.
 -/
+@[inline]
 def back! [Inhabited α] (xs : Array α) : α :=
   xs[xs.size - 1]!
 
@@ -386,6 +387,7 @@ Returns the last element of an array, given a proof that the array is not empty.
 See `Array.back!` for the version that panics if the array is empty, or `Array.back?` for the
 version that returns an option.
 -/
+@[inline]
 def back (xs : Array α) (h : 0 < xs.size := by get_elem_tactic) : α :=
   xs[xs.size - 1]'(Nat.sub_one_lt_of_lt h)
 
@@ -395,6 +397,7 @@ Returns the last element of an array, or `none` if the array is empty.
 See `Array.back!` for the version that panics if the array is empty, or `Array.back` for the version
 that requires a proof the array is non-empty.
 -/
+@[inline]
 def back? (xs : Array α) : Option α :=
   xs[xs.size - 1]?