Sandbox needed for WIE-MIP simulations

Given the tight timeline requested for WIE-MIP simulation (June 2026) I thought it would be help to track details of the model setup we'll need. This may end up being the parent issue that references other tasks that are needed. It also could end up being it's own project board. The project is basically set up like TRENDY (with constant land use)+ future scenarios:

1. Spinup (1850 land use, CO2 & NDEP)
2. Idealized experiments to diagnose TCRE
- Control (extend spinup)
- BGC (1% CO2 for BGC + control climate)
- COU (fully coupled 1% CO2 for BGC & Climate) *uses 3 DATM variants
- RAD (optional)
2b. Ongoing discussion in WIEMIP about turning off features (e.g. N or fire), retuning?, and repeating spinup and 1% experiments
3. HIST? (constant land use)
4. Scenario MIP extensions (2025-2300)
- 4 scenarios * 3 DATM variants

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Here's an on going list for what we may need:
- [x] **Branch tag:** We'll want Sean's hillslope hydrology / methane branch brought up to the current master tag see #3906
- [x] **Surface Dataset**, see #3912
- [x] **DATM**: Supplied by WIE-MIP, which has both 0.5 degree and 1.0 degree options with 6 hr resolution
- Check that we're using direct and diffuse DATM see #3935
- [x] **Aerosols, NDEP, population density**, these can be 1850, although WIE-MIP has it's own NDEP data?
- constant 1850 aerosol, popdens & ozone.
- constant 1850 NDEP data is proposed BGC and COU cases (see also #3961)
- use this notebook from Adrianna's TRENDY work to create N-dep streams `/glade/work/afoster/TRENDY/trendyclm/driver_data_creation/TRENDY_Data_Prep.ipynb`
- [x] **CO2**, need 1% CO2 data for idealized simulations & scenarioMIP data for future scenarios. see #3936
- [x] **Parameter file**, ideally using the latest from CLM6, but may need CH4 and fire tunings and others from @swensosc?
- Testing this in the 'flat' case in [LMWG_dev#156](https://github.com/NCAR/LMWG_dev/issues/156) and now [158](https://github.com/NCAR/LMWG_dev/issues/158).
- using `/glade/work/wwieder/modified_inputs/ctsm60_params.genericCropFix.ch4cal_d.c260410.nc`
- This **SOULD BE NEW DEFAULT** CLM6 parameter file?
- **Latest being used in [LMWG_dev#164](https://github.com/NCAR/LMWG_dev/issues/164)**
- Need to calibrate for hillslope, YES, both fire and CH4 will need to be calibrated (see [LMWG_dev#160](https://github.com/NCAR/LMWG_dev/issues/160) & [discussion 162](https://github.com/NCAR/LMWG_dev/discussion/162))
- using `/glade/u/home/fangli/ctsm60_params.genericCropFix.ch4cal_e.fire.c260424.nc`
- **Latest being used in [LMWG_dev#165](https://github.com/NCAR/LMWG_dev/issues/165)**
- This **SOULD BE NEW DEFAULT** CLM6_HillslopeHydrology parameter file?
- [ ] **User Mods** to set this all up, including history fields and frequency being requested
- see #3949
- see #3950
- [x] **MEGAN** evaluate if we should be using `megan_use_gamma_sm = .false.` for WIEMIP
- [ ] **Post processing** scripts to generate single variable time series, convert units, rename variables per TRENDY & regrid to regular 1 degree dataset.
- Build this off [Adrianna's TRENDY workflow](https://github.com/adrifoster/trendyclm/tree/main)

Lot's of people have experience here or can help
@adrifoster, @swensosc, @lawrencepj1, @linniahawkins, @dlawrenncar, @ekluzek, @slevis-lmwg, @olyson