feat(vsock): DCGM-5059 Add VSOCK standalone routing via dcgmConnect_v3

[rvatkar]

Adds dcgmConnect_v3 support for standalone DCGM connection strings in go-dcgm.
This change detects supported DCGM URI schemes:

tcp://
unix://
vsock://

When dcgm.Init(dcgm.Standalone, ) receives one supported URI argument, it routes through dcgmConnect_v3. Existing legacy standalone calls, such as host/port plus socket flag, continue to use the existing dcgmConnect_v2 path.

Validation

• Added unit coverage for VSOCK, TCP, UNIX, uppercase schemes, legacy host/socket flag behavior, missing socket flag behavior, and unsupported scheme fallthrough.
• Added runtime symbol guard for dcgmConnect_v3 to return a clear error if the deployed libdcgm.so.4 is too old.
• Verified locally:
  • go test ./pkg/dcgm -count=1

Notes

• Requires runtime DCGM library version that exports dcgmConnect_v3.
• This MR preserves existing dcgmConnect_v2 behavior for legacy standalone connection arguments.

[nccurry]

LGTM