Use a longer backoff for CASE retries.

[bzbarsky-apple]

We have a common failure mode for Thread devices where the commissioner sends Sigma1 prior to sending CommissioningComplete, the commissionee responds, but the Sigma2 (and all its retries) never reach the commissioner.

When this happens, our existing CASE retries do not help because they happen too quickly: the commissionee is waiting for Sigma3, and will ignore Sigma1 messages until it gets the Sigma3 or times out.

To address this, include the time it would take the commissionee to time out in our CASE retry delay for every other retry. This allows us to retry quickly once, then give the commissionee time to start listening again, then retry quickly one or two times (depending on how many retries were requested), etc.

[github-actions]

PR #25736: Size comparison from bbb8e93 to 55d3f52

Increases (1 build for cc32xx)

platform	target	config	section	bbb8e93	55d3f52	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL	(read only)	645489	645601	112	0.0
			.debug_aranges	87392	87400	8	0.0
			.debug_frame	300284	300316	32	0.0
			.debug_info	20246022	20248011	1989	0.0
			.debug_line	2661031	2661469	438	0.0
			.debug_loc	2804874	2805592	718	0.0
			.debug_ranges	283152	283208	56	0.0
			.debug_str	3027037	3027174	137	0.0
			.strtab	380331	380421	90	0.0
			.symtab	257376	257408	32	0.0
			.text	537376	537488	112	0.0

Full report (1 build for cc32xx)

platform	target	config	section	bbb8e93	55d3f52	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	645489	645601	112	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	930289	930289	0	0.0
			.debug_aranges	87392	87400	8	0.0
			.debug_frame	300284	300316	32	0.0
			.debug_info	20246022	20248011	1989	0.0
			.debug_line	2661031	2661469	438	0.0
			.debug_loc	2804874	2805592	718	0.0
			.debug_ranges	283152	283208	56	0.0
			.debug_str	3027037	3027174	137	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	380331	380421	90	0.0
			.symtab	257376	257408	32	0.0
			.text	537376	537488	112	0.0

[nivi-apple]

Looks good to me.