feat(18-01): add gosnmp dependency, SNMP types, and client builder

- Install gosnmp v1.43.2 as direct dependency
- Create snmp package with SNMPConfig, CompiledProfile, PollGroup types
- Implement BuildSNMPClient for v1, v2c, and v3 (all security levels)
- Map auth protocols (MD5, SHA, SHA224-512) and priv protocols (DES, AES128-256)
- MaxRepetitions set to 10 (not gosnmp default 50) for embedded devices
- Full test coverage: 9 tests covering all SNMP versions and protocol mappings

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

poller/go.sum

@@ -67,6 +67,8 @@ github.com/google/go-tpm v0.9.8 h1:slArAR9Ft+1ybZu0lBwpSmpwhRXaa85hWtMinMyRAWo=
 github.com/google/go-tpm v0.9.8/go.mod h1:h9jEsEECg7gtLis0upRBQU+GhYVH6jMjrFxI8u6bVUY=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
 github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/gosnmp/gosnmp v1.43.2 h1:F9loz6uMCNtIQj0RNO5wz/mZ+FZt2WyNKJYOvw+Zosw=
+github.com/gosnmp/gosnmp v1.43.2/go.mod h1:smHIwoaqr1M+HTAEd7+mKkPs8lp3Lf/U+htPUql1Q3c=
 github.com/grpc-ecosystem/grpc-gateway/v2 v2.28.0 h1:HWRh5R2+9EifMyIHV7ZV+MIZqgz+PMpZ14Jynv3O2Zs=
 github.com/grpc-ecosystem/grpc-gateway/v2 v2.28.0/go.mod h1:JfhWUomR1baixubs02l85lZYYOm7LV6om4ceouMv45c=
 github.com/hashicorp/golang-lru/v2 v2.0.7 h1:a+bsQ5rvGLjzHuww6tVxozPZFVghXaHOwFs4luLUK2k=