Split errors in Tool check

[chshersh]

Currently, the checkTool function has the following type:

checkTool :: cmd -> Tool cmd -> IO ToolCheckResult

where ToolCheckResult is defined as follows:

data ToolCheckResult
    = ToolNotFound Text
    | ToolWrongVersion Text
    | ToolOk

A value of ToolCheckResult is thrown as an exception here:

https://github.com/chshersh/iris/blob/6be65d46a5b3f2cabd09dedbc88045c4be4fb224/src/Iris/Env.hs#L138-L141

This is suboptimal because the result can never have the ToolOk constructors but we're forcing downstream users to handle this case.

So we want to split success and error cases in the ToolCheckResult type.