fujinet: add commands and recipe support

[DrPitre]

Summary

• add a first set of FujiNet utility commands
• wire those commands into the WildBits and CoCo 3 command builds
• add FUJINET=1 support to the shared CoCo 3 recipes
• teach the shared recipe library build to produce libfuji.a

New commands

• fnlisthosts
• fngethost
• fnsethost
• fnlistdevs
• fnmount
• fnstatus

These build alongside the existing fngetdevfile and fnsetdevfile commands.

Recipe support

With this change, shared CoCo 3 recipes can include the FujiNet command set by enabling:

FUJINET=1

This works for both the standard CoCo 3 recipe and the DriveWire-oriented recipe.

Verification

• assembled and linked the new FujiNet commands in the WildBits command trees
• dry-ran recipes/coco3/40d with FUJINET=1
• dry-ran recipes/coco3/dw with FUJINET=1
• confirmed the recipe path builds libfuji.a and copies the FujiNet commands into CMDS