Phase 1-2: Migrate to Deno with npm: and node: specifiers

- Created deno.json configuration
- Updated all imports to use npm:net-snmp@3.20.0
- Changed all Node.js built-in imports to node: specifiers
- Updated all .js extensions to .ts in imports
- Created mod.ts as Deno entry point
- Ready for Phase 3: CLI simplification

ts/snmp/oid-sets.ts

@@ -1,4 +1,4 @@
-import type { IOidSet, TUpsModel } from './types.js';
+import type { IOidSet, TUpsModel } from './types.ts';
 
 /**
  * OID sets for different UPS models