Update Level 1b consumable availability to reflect 1b-2 merge

[sakshimohan]

This PR updates the RF for consumable availability for level 1b facilities to reflect the merging of level 1b and 2 in simulations.

[sakshimohan]

Availability at level 1b is updated with average of availability (by item_code and month) for levels 1b and 2. Three strategies of weighting are adopted to test calibration -

1. level2 – fully replace Level 1b availability with Level 2 values.

New RF :ResourceFile_Consumables_availability_small_level2.csv

2. national_1b_to_2_ratio – apply a single national-level 1b:2 facility ratio for weighting.

New RF :ResourceFile_Consumables_availability_small_national_1b_to_2_ratio.csv

3. district_1b_to_2_ratio – apply district-specific 1b:2 ratios for weighting.

New RF : ResourceFile_Consumables_availability_small_district_1b_to_2_ratio.csv

ResourceFile_Consumables_availability_small contains the original level 1b and 2 availability.

[sakshimohan]

Hi @tbhallett. As discussed earlier this week, I've added three new versions of the consumable availability RF on this branch to see how each of these performs in comparison with data.
The average availability by level in the 4 cases is as follows -

Level	Actual	level2	national_1b_to_2_ratio	district_1b_to_2_ratio
0	0.22	0.22	0.22	0.22
1a	0.44	0.44	0.44	0.44
1b	0.58	0.70	0.61	0.63
2	0.70	0.70	0.70	0.70
3	0.79	0.79	0.79	0.79
4	0.38	0.38	0.38	0.38