Revert "[BBT-110] Remove string handling in spacing styles component"

[g-elwell]

Reverts #38

More back and forth on this one - once the fix was removed I seem to have hit this issue again.

It appears to be coming from the button element styles on my install. They are defined as follows in the TT3 theme:

"spacing": {
	"padding": {
		"top": "min(1rem, 3vw) !important",
		"right": "min(2.75rem, 6vw) !important",
		"bottom": "min(1rem, 3vw) !important",
		"left": "min(2.75rem, 6vw) !important"
	}
}

However they are showing up in the application as:

{padding: 'calc(0.667em + 2px) calc(1.333em + 2px)'}

Unsure how/when the styles are implemented, but I have confirmed they are present in the base config pulled from __experimentalGetCurrentThemeBaseGlobalStyles. Using WordPress 6.4.

Reverting this to add the safeguard back in for now until we can investigate a proper fix.