Calculator tools: Missing units and incorrect symbol

Description

There are no units present for the input boxes for ρ, which is not a dimensionless quantity. Going by the values provided for copper and other common metals, it appears the values are expected to be given in units of Ω·m, but unlike all other dimensioned input quantities, no unit is specified.

Likewise, the values for μ(substrate) and μ(conductor) appear to be intended as unitless relative values, in which case the symbols should actually be μr(substrate) and μr(conductor) (strictly speaking, the r in both this and εr should be subscript, but I recognise that that's not trivial to do with ordinary GUI toolkits).

Current:	(badly) corrected mockup:

KiCad Version

Application: KiCad Calculator Tools x64 on x64

Version: 8.0.7, release build

Libraries:
	wxWidgets 3.2.6
	FreeType 2.13.3
	HarfBuzz 10.0.1
	FontConfig 2.15.0
	libcurl/8.10.1-DEV Schannel zlib/1.3.1

Platform: Windows 10 (build 19045), 64-bit edition, 64 bit, Little endian, wxMSW

Build Info:
	Date: Dec  3 2024 15:58:01
	wxWidgets: 3.2.6 (wchar_t,wx containers)
	Boost: 1.86.0
	OCC: 7.8.1
	Curl: 8.10.1-DEV
	ngspice: 43
	Compiler: Visual C++ 1939 without C++ ABI

Build settings: