Add custom function to export QLoRA models

[caroteu]

@anwai98
The results for covid_if on this branch are

Dataset	Method	Base Model	AIS	Single Box	Single Point	IB	IP
covid_if	Vanilla	vit_b		0.269202	0.005474	0.089099	0.023185
	Generalist	vit_b_lm	0.112116	0.538591	0.094117	0.808333	0.698748
	Full_FT	vit_b	0.296931	0.546952	0.214309	0.735064	0.624448
		vit_b_lm	0.318951	0.563352	0.225422	0.826157	0.746941
	LoRA	vit_b	0.262948	0.560446	0.146677	0.751644	0.657821
		vit_b_lm	0.304090	0.609217	0.217692	0.837911	0.769527
	QLoRA	vit_b	0.254248	0.499999	0.057334	0.140361	0.025651
		vit_b_lm	0.308042	0.605862	0.232271	0.832002	0.752714

Which is consistent with the previous results

Dataset	Method	AIS	Single Box	Single Point	IB	IP
covid_if	Previous QLoRA	0.254248	0.500000	0.057334	0.140055	0.026356
		0.308042	0.605862	0.232271	0.833025	0.753349

[anwai98]

Awesome. Looks good to me. Good job @caroteu! ;)

I'll go ahead and merge this to our running PR already!