Within keyword fails to compare wrapped types and null

[BernieWhite]

Description of the issue

When using the Within keyword, comparison of wrapped non-string types incorrectly returns Fail instead of Pass.

In addition comparison against null also fails.

To Reproduce

Steps to reproduce the issue:

Rule 'WithinTypes' {
    Within 'BooleanValue' $True
    Within 'IntValue' 0, 1, 2, 3
    Within 'NullValue' $Null
}

$testObject = @(
    [PSCustomObject]@{ BooleanValue = $True; IntValue = 1; NullValue = $Null; }
    [PSCustomObject]@{ BooleanValue = $False; IntValue = 100; NullValue = $Null; }
    ([PSCustomObject]@{ BooleanValue = $True; IntValue = 1; NullValue = $Null; } | ConvertTo-Json | ConvertFrom-Json)
    [PSCustomObject]@{ BooleanValue = $Null; IntValue = $Null; NullValue = 'NotNull'; }
)

$testObject | Invoke-PSRule -Name 'WithinTypes' -Outcome All;

Expected behaviour

Within should correctly compare non-string types.

Module in use and version:

• Module: PSRule
• Version: 0.7.0

Captured output from $PSVersionTable:

Name                           Value
----                           -----
PSVersion                      6.2.1
PSEdition                      Core
GitCommitId                    6.2.1
OS                             Microsoft Windows 10.0.18362
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Additional context

Additional cases related to #226.