New default namelist for tracer_cnst, prescribed_ozone / prescribed_strataero, and stream_ndep_data

Hi @tilmes and Shawn,

We would like to put the settings and forcing files we are currently using onto the trunk. This includes the latest `tracer_cnst`, `prescribed_ozone` / `prescribed_strataero`, and `stream_ndep_data` files, as well as several CAM7 namelist settings.

To put the current settings on the trunk, **we need answers to all questions below.** Thanks a bunch!

Here is the `user_nl_cam` configuration used in our recent runs:

```text
tracer_cnst_datapath = '/glade/derecho/scratch/shawnh/Forcings_tmp/20260706/b.e30_alpha09b.B1850C_MTt4s.ne30_t233_wgx3.360/atm/proc/TracerCnstFileCyclic1850'
tracer_cnst_file = 'tracer_cnst_MTt4s_halons_3Dmonthly_1850climo360_c20260706.nc'

prescribed_ozone_datapath = '/glade/derecho/scratch/shawnh/Forcings_tmp/20260706/b.e30_alpha09b.B1850C_MTt4s.ne30_t233_wgx3.360/atm/proc/ozone_strataero_day_5_zm'
prescribed_ozone_file = 'ozone_strataero_b.e30_alpha09b.B1850C_MTt4s.ne30_t233_wgx3.360_1850_0005_0030_transient_zm_5day_c20260706.nc'

prescribed_strataero_datapath = '/glade/derecho/scratch/shawnh/Forcings_tmp/20260706/b.e30_alpha09b.B1850C_MTt4s.ne30_t233_wgx3.360/atm/proc/ozone_strataero_day_5_zm'
prescribed_strataero_file = 'ozone_strataero_b.e30_alpha09b.B1850C_MTt4s.ne30_t233_wgx3.360_1850_0005_0030_transient_zm_5day_c20260706.nc'

stream_ndep_data_filename = '/glade/derecho/scratch/shawnh/Forcings_tmp/20260911/b.e30_alpha09b.B1850C_MTt4s.ne30_t233_wgx3.360/atm/proc/NDepositionCyclic1850/fndep_clm_MTt4s_3Dmonthly_1850climo360_c20260911.nc'
```

## To put these on the trunk, we need to:

1. **Copy the files into the CESM inputdata repository.**
2. **Update the namelist defaults and the appropriate use cases.**

## Modification of use cases

I assume the only use cases that need to be modified are the pre-industrial LTso and MTso use cases:

```text
1850_cam_lt.xml
1850_cam_mt.xml
```

**Could you confirm this is correct?**

## Where we are planning to put the new input files

### `tracer_cnst`

We were planning to put:

```text
tracer_cnst_MTt4s_halons_3Dmonthly_1850climo360_c20260706.nc
```

under:

```text
/glade/campaign/cesm/cesmdata/cseg/inputdata/atm/cam/tracer_cnst
```

**Is this location OK with you, or should we create/use a `TracerCnstFileCyclic1850` subdirectory, corresponding to the current directory structure?**

### Ozone / stratospheric aerosols

We were planning to put:

```text
ozone_strataero_b.e30_alpha09b.B1850C_MTt4s.ne30_t233_wgx3.360_1850_0005_0030_transient_zm_5day_c20260706.nc
```

under:

```text
/glade/campaign/cesm/cesmdata/cseg/inputdata/atm/cam/ozone_strataero
```

**Is this location OK with you, or should we create/use an `ozone_strataero_day_5_zm` subdirectory?**

### N deposition

For N deposition, we are more puzzled about where the file should go.

The new file is:

```text
fndep_clm_MTt4s_3Dmonthly_1850climo330_c20260706.nc
```

It looks like these N deposition files have historically been stored under the CLM inputdata directory:

```text
/glade/campaign/cesm/cesmdata/cseg/inputdata/lnd/clm2/ndepdata
```

Also, since `stream_ndep_data_filename` is now defined through the CAM namelist, Cheryl was wondering whether the file should instead be placed somewhere under the CAM inputdata directory.

**What do you recommend?**

**Also, should we create/use an `NDepositionCyclic1850` subdirectory there?**

Thanks,

@cecilehannay , @cacraigucar , and @PeterHjortLauritzen