Please remember last input at length tuning dialog

Description

Currently each length tuning starts with 100mm as default. It would be handy to remember the last user input.

Steps to reproduce

KiCad Version

Application: KiCad PCB Editor x64 on x64

Version: 7.99.0-3268-g68a5753c80, release build

Libraries:
	wxWidgets 3.2.3
	FreeType 2.12.1
	HarfBuzz 8.2.1
	FontConfig 2.14.2

Platform: Windows 11 (build 22621), 64-bit edition, 64 bit, Little endian, wxMSW

	wxWidgets: 3.2.3 (wchar_t,wx containers)
	Boost: 1.83.0
	OCC: 7.7.1
	Curl: 8.4.0-DEV
	ngspice: 41
	Compiler: Visual C++ 1936 without C++ ABI

Build settings: