zero foi truncated for some ages or years based on epi knowledge

[zmcucunuba]

In the foi chunks, we need to incorporate something like a vector with zero-truncated values.

First example: HPV This is a sexually transmitted infection, so we should restrict FOI to 0 for ages before sexual debut.

Age	Chunk	Is_zero
1	1	yes
2	1	yes
3 …	1	yes
15	2	no

Second example: CHIK

Similarly, for time-varying models. An example of this is Chikungunya virus in the Americas. We have good evidence that it didn't circulate in the human population before 2010.

Year | Chunk | Is_zero

Year	Chunk	Is_zero
2000	1	yes
2001	1	yes
…	1	yes
2010	2	no

Tagging @ekamau ;)

[zmcucunuba]

This has been implemented in #190 in the function set_sero_model using the parameter foi_windows