Fix #2722: Add missing Because parameter to Should-BeSlowerThan (#2727)

* Fix #2722: Add missing Because parameter to Should-BeSlowerThan and fix flaky test

Should-BeSlowerThan referenced $Because in error messages but never
declared it as a parameter, so it was always null.

Also changed the Should-BeFasterThan Because test to use a deterministic
[timespan] instead of a scriptblock with Start-Sleep to avoid timing
flakiness on CI.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Verify Because message appears in assertion error

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: nohwnd

src/functions/assert/Time/Should-BeSlowerThan.ps1

@@ -51,7 +51,8 @@
         [Parameter(Position = 1, ValueFromPipeline = $true)]
         $Actual,
         [Parameter(Position = 0)]
-        $Expected
+        $Expected,
+        [string] $Because
     )
 
     if ($Expected -isnot [timespan]) {

tst/functions/assert/Time/Should-BeFasterThan.Tests.ps1

@@ -49,8 +49,9 @@ Describe "Should-BeFasterThan" {
     }
 
     It "Has Because parameter" -ForEach @(
-        @{ Actual = { Start-Sleep -Milliseconds 10 }; Expected = "1ms"; Because = "I said so" }
+        @{ Actual = [timespan]::FromMilliseconds(100); Expected = "1ms"; Because = "I said so" }
     ) {
-        { $Actual | Should-BeFasterThan -Expected $Expected -Because $Because } | Verify-AssertionFailed
+        $err = { $Actual | Should-BeFasterThan -Expected $Expected -Because $Because } | Verify-AssertionFailed
+        $err.Exception.Message | Verify-Like '*because I said so*'
     }
 }

tst/functions/assert/Time/Should-BeSlowerThan.Tests.ps1

@@ -24,4 +24,11 @@ Describe "Should-BeSlowerThan" {
     ) {
         { $Actual | Should-BeSlowerThan -Expected $Expected } | Verify-AssertionFailed
     }
+
+    It "Has Because parameter" -ForEach @(
+        @{ Actual = [timespan]::FromMilliseconds(1); Expected = "1000ms"; Because = "I said so" }
+    ) {
+        $err = { $Actual | Should-BeSlowerThan -Expected $Expected -Because $Because } | Verify-AssertionFailed
+        $err.Exception.Message | Verify-Like '*because I said so*'
+    }
 }