fix(keys): spacebar now sends a KeySpace

[bashbunni]

This fixes a bug where the spacebar would send a Key with type KeyRunes instead of KeySpace. The Runes portion of Key will still contain a space after this fix.

// This is what is sent when you press spacebar now
type Key struct {
    Type: KeySpace,
    Runes: []rune{' '},
}

---

Changes:

• remove keySP
• assign KeySpace to " "
• update tests to expect " " instead of "space"

I didn't make any changes to readInput.
Manually tested KeySpace in addition to the tests with no issues and KeySpace worked as expected

[meowgorithm]

Thank you, @bashbunni!