External Model

[goreaditya]

External station 6002 is currently missing from the network.
The updated external model input seed matrix is incorrect—it matches the dimensions of internal zones only and does not include any external stations.
Similarly, the externals.csv input file has been incorrectly updated and lists internal zones as external stations.
These issues need to be investigated and resolved to ensure the external model functions correctly.

[goreaditya]

There were three issues noticed.

1. The external node 6002 was disconnected.
2. The seed matrix, after the taz update, didn't include any of the external stations 6001-6035.
3. The externals.csv was incorrectly updated with external zones instead of external stations.

@JimSullivan8997 please address these issues in your commit.