eeschema: backslash-escaped ${ and @{ prevent other expansions

Description

This might be WAI. If you backslash-escape @ or $ and follow it with a {, subsequent expansions will not happen until the matched }. On the one hand, this makes writing examples easy since only the outer level needs to be "disabled" with an escape. On the other hand, if for some reason you wanted to write ${ without affecting anything else, it's impossible with the currently available syntax, afaikt (attempts to do so by embedding strings in @{ } blocks induce all sorts of strange behavior, but maybe I'm not being creative enough. \@@{"$"}{ for example expands to \@ somehow).

Steps to reproduce

1. Create a textbox with ${#} \@{${#} ${#}} ${#}
2. Result is 1 @{${#} ${#}} 1 but perhaps it should be 1 @{1 1} 1?

KiCad Version

Application: KiCad Schematic Editor x86_64 on x86_64

Version: 9.99.0-4324-g39cf28d5fd, release build

Libraries:
	wxWidgets 3.2.4
	FreeType 2.11.1
	HarfBuzz 2.7.4
	FontConfig 2.13.1

Platform: Ubuntu 22.04.5 LTS, 64 bit, Little endian, wxGTK, X11, xubuntu, x11
OpenGL: Intel, Mesa Intel(R) Graphics (RPL-P), 4.6 (Compatibility Profile) Mesa 23.2.1-1ubuntu3.1~22.04.3

	wxWidgets: 3.2.4 (wchar_t,wx containers) GTK+ 3.24
	Boost: 1.74.0
	OCC: 7.6.3
	Curl: 7.81.0
	ngspice: 43
	Compiler: Clang 20.1.8 with C++ ABI 1002
	KICAD_IPC_API=ON
	KICAD_USE_PCH=OFF

Locale: 
	Lang: en_US
	Enc: UTF-8
	Num: 1,234.5
	Encoded кΩ丈: D0BACEA9E4B888 (sys), D0BACEA9E4B888 (utf8)