Getting Hector set up for H2 emissions

[kdorheim]

This PR is just to set Hector up for the H2 work, mainly to address #748 and #750, I am not sure if everything will make its way into the final release but

• added tau oh as a variable that can be fetched from the R interface (should be pretty helpful during dev)
• registered H2 emissions as input to the OH component
• H2 emissions set to 0 for all input csv tables as the moment
• Added a H2 unit test (again this is useful during the dev phase and might be reorganized)

Things to confirm with others

• H2 units - Tg?

[github-actions]

Differences in Hector outputs

Hello, this is leeyabot!

The current pull request's outputs do not differ from 3.1.1 (d931a00).

[kdorheim]

Demonstrating OH lifetime is reported as output

 ini <- system.file("input/hector_ssp245.ini", package = "hector")
dates <- 1750:2100

 hc <- newcore(ini)
 run(hc)
 out <- fetchvars(hc, dates = 1750:2100, vars = LIFETIME_OH())

head(out)

>     head(out)
             scenario year variable    value units
1 Unnamed Hector core 1750   TAU_OH 6.656159 Years
2 Unnamed Hector core 1751   TAU_OH 6.662276 Years
3 Unnamed Hector core 1752   TAU_OH 6.668394 Years
4 Unnamed Hector core 1753   TAU_OH 6.678406 Years
5 Unnamed Hector core 1754   TAU_OH 6.691402 Years
6 Unnamed Hector core 1755   TAU_OH 6.694948 Years

[github-actions]

Differences in Hector outputs

Hello, this is leeyabot!

The current pull request's outputs do not differ from 3.1.1 (d931a00).

[kdorheim]

H2 emissions can be changed but do not affect Hector's behavior yet...

[bpbond]

Thanks for the good prep work!