feat: Schema checker script

chore: add NX3 as a registry
--- a/data/registry/NX3
+++ b/data/registry/NX3
@ -0,0 +1,4 @@
 registry:       NX3
 url:            https://git.brettb.xyz/nx3/registry
 mnt-by:         NX3-MNT
 source:         NX3
--- a/utils/schema-check/nx3_schema_local.py
+++ b/utils/schema-check/nx3_schema_local.py
Author	SHA1	Message	Date
Brett Bender	2f8cec54c1	feat: Schema checker script	11 months ago
Brett Bender	b0b315dcd9	chore: add NX3 as a registry	11 months ago