Reduce CPU usage of chip-console

[mspang]

This is busy polling the serial port, and as a result uses 100% CPU. Use a non-zero timeout to avoid this.

Using asyncio would be better, but pyserial support for this is still experimental.

[github-actions]

PR #25663: Size comparison from d04e396 to a7edd15

Full report (1 build for cc32xx)

platform	target	config	section	d04e396	a7edd15	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	645097	645097	0	0.0
			(read/write)	203848	203848	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197248	197248	0	0.0
			.comment	194	194	0	0.0
			.data	1480	1480	0	0.0
			.debug_abbrev	930293	930293	0	0.0
			.debug_aranges	87384	87384	0	0.0
			.debug_frame	300248	300248	0	0.0
			.debug_info	20245939	20245939	0	0.0
			.debug_line	2660971	2660971	0	0.0
			.debug_loc	2804896	2804896	0	0.0
			.debug_ranges	283168	283168	0	0.0
			.debug_str	3026947	3026947	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	105993	105993	0	0.0
			.shstrtab	232	232	0	0.0
			.stab	204	204	0	0.0
			.stabstr	441	441	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	379204	379204	0	0.0
			.symtab	256912	256912	0	0.0
			.text	536984	536984	0	0.0