chip-repl hits the Code is unsafe/racy assert when BLE commissioning is started

[tehampson]

Fixes: #26265

PR #26180 added assert on the task ownership of the chip Stack lock on some SystemLayer timer calls.

The Linux ChipDeviceScanner starts a SystemLayer timer on the BLE connection which now asserts.

This pr fix the assert on SystemLayer().StartTimer call by acquiring the chipStack Lock before the call (and releasing it after)

Tested the fix by successfully starting to scan chip-repl

[github-actions]

PR #26338: Size comparison from 8f66f42 to 22d4958

Increases (1 build for cc32xx)

platform	target	config	section	8f66f42	22d4958	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL	.debug_info	19511283	19511285	2	0.0

Full report (1 build for cc32xx)

platform	target	config	section	8f66f42	22d4958	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	604426	604426	0	0.0
			(read/write)	204156	204156	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197568	197568	0	0.0
			.comment	206	206	0	0.0
			.data	1468	1468	0	0.0
			.debug_abbrev	956872	956872	0	0.0
			.debug_aranges	101056	101056	0	0.0
			.debug_frame	341168	341168	0	0.0
			.debug_info	19511283	19511285	2	0.0
			.debug_line	2664965	2664965	0	0.0
			.debug_line_str	513	513	0	0.0
			.debug_loc	33340	33340	0	0.0
			.debug_loclists	1486884	1486884	0	0.0
			.debug_ranges	4984	4984	0	0.0
			.debug_rnglists	94239	94239	0	0.0
			.debug_str	3068127	3068127	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	104298	104298	0	0.0
			.shstrtab	265	265	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	480350	480350	0	0.0
			.symtab	287024	287024	0	0.0
			.text	498004	498004	0	0.0