Second major code overhaul of 2026
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Implement the planned changes to "extresist":

(1) Remove the .sim format as a requirement.
    extresist will get its node list from doing
    a standard extraction (extFindNodes() or
    ExtFindRegions(), whichever is appropriate.
    This should be able to be done as a relatively
    simple change, allowing "extresist" to be used
    without doing "ext2sim" as part of the process.

(2) Move extresist into the "extract" code.
    "extresist" will become a command "extract do
    extresist" and "ext2spice extresist on|off"
    will determine if split nodes and terminals
    are kept apart in the final netlist or
    aggregated---Exactly as capacitance is done
    now.

    Need to figure out how "tile junk" client data
    and extract client data can exist simultaneously.

    "extresist" will run within "extBasic", being
    called on a node after the devices and nodes are
    identified;  nodes created by ExtFindRegions()
    will get sub-divided into more nodes.  The
    difficult case will be where a single tile gets
    multiple nodes (such as where other wires branch
    off the tile in the up or down direction).  Maybe
    this can be done like ClientData for split tiles,
    with an indicator bit in ti_body?
    
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