Geolocation: Add OutboundIcmp target type to onchain program, SDKs, and CLI

[ben-dz]

Parent: #3404

Add a new OutboundIcmp target type (= 2) across the onchain program, SDKs, and CLI. This type is like Outbound (uses an IPv4 address) but instructs the geoprobe-agent to use ICMP pings instead of TWAMP probes. It does not need a location_offset_port or TWAMP port.

Changes

Smart Contract (smartcontract/programs/doublezero-geolocation/)

• state/geolocation_user.rs: Add OutboundIcmp = 2 to GeoLocationTargetType enum. Update Display impl.
• processors/geolocation_user/add_target.rs: Validate OutboundIcmp targets the same as Outbound (public IPv4 required), but location_offset_port should be 0 (unused) and target_pk should be default.
• processors/geolocation_user/remove_target.rs: Handle OutboundIcmp in target matching (same as Outbound — match by IP address).
• Unit + integration tests: Add OutboundIcmp test cases for add, remove, serialization round-trip.

Rust SDK (smartcontract/sdk/rs/)

• geolocation/geolocation_user/add_target.rs: Add validation branch for OutboundIcmp (require public IP, reject non-default target_pk).
• geolocation/geolocation_user/remove_target.rs: Handle OutboundIcmp in remove validation.

Rust CLI (smartcontract/cli/)

• geolocation/user/add_target.rs: Add OutboundIcmp to the TargetType clap enum. For OutboundIcmp, require --target-ip, reject --target-pk, and don't require --target-port.
• geolocation/user/remove_target.rs: Add OutboundIcmp to the TargetType enum and handle it like Outbound (match by IP).
• geolocation/user/get.rs: Display OutboundIcmp targets correctly in TargetDisplay.

Go SDK (sdk/geolocation/go/)

• state.go: Add GeoLocationTargetTypeOutboundIcmp = 2. Update String() and deserialization validation bound.
• state_test.go: Add round-trip and string tests for the new type.

Acceptance

• doublezero geolocation user add-target --type outbound-icmp --target-ip 8.8.8.8 --probe <probe> succeeds
• doublezero geolocation user get --user <code> shows the target as type outbound-icmp
• Go SDK deserializes OutboundIcmp targets without error
• All existing tests still pass