[mobile config] track asset ownership. Add owner info to grpc response (part 2)

[kurotych]

Previous PR: #1102

Add info_stream_v4 GRPC endpoint

• to response: owner and owner_changed_at
• to request: min_owner_changed_at filter

Remove (oneshot) backfill_gateway_owners

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GRPC endpoint
Could be tested manually on branch mobile-config-cli-gateway-info4-test

test command exmpl:
./target/debug/mobile-config-cli --log-filter=Debug --config-host http://localhost:8090 --config-pubkey 13L4aDqCvji18g1uUqirM96Y9y67FyDLsV7C986sGTdCNCmYFeG --keypair ./config-server-keypair.
bin gateway info-stream-v4 --min-owner-changed-at 1769627776 --batch-size 5000

[Copilot]

Pull request overview

This PR implements the second stage of asset ownership tracking by exposing owner information through a new GRPC endpoint and removing the one-time backfill function. Building on PR #1102 which added owner tracking to the database, this change makes owner data available to API consumers and completes the migration.

Changes:

• Added info_stream_v4 GRPC endpoint that returns gateway information including owner and owner_changed_at fields with filtering support
• Updated tracker logic to properly update last_changed_at when owner changes (previously only hash changes triggered this)
• Removed one-time backfill function backfill_gateway_owners and its associated test now that migration is complete

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
mobile_config/tests/integrations/main.rs	Adds gateway_service_v4 test module
mobile_config/tests/integrations/gateway_tracker.rs	Removes backfill test and updates assertion to verify last_changed_at is updated when owner changes
mobile_config/tests/integrations/gateway_service_v4.rs	Comprehensive tests for v4 endpoint including basic functionality, NULL owner filtering, and min_owner_changed_at filtering
mobile_config/src/gateway/tracker.rs	Removes backfill function and updates last_changed_at logic to trigger on owner changes
mobile_config/src/gateway/service/mod.rs	Implements info_stream_v4 endpoint with owner filtering support
mobile_config/src/gateway/service/info_v4.rs	New module defining GatewayInfoV4 struct with owner fields and conversions
mobile_config/src/gateway/db.rs	Adds stream_gateway_info_v4 query function with owner_changed_at filtering
Cargo.toml	Patches proto dependencies to use gateway-info-v4 branch
Cargo.lock	Updates dependency versions to gateway-info-v4 branch

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