feat(sdk): early runtime host binding for dialog + listAvailableEncodings vector helper

[pabloinigoblasco]

Summary

Enable plugins to query available encodings before the dialog is shown by introducing a two-phase runtime host binding pattern.

Problem

The original listAvailableEncodings() added in PR #27 was callable only after bindRuntimeHost(), which happens AFTER the dialog closes. Plugins like MQTT/ZMQ need this information to populate their encoding combo boxes during widget_data().

Solution: Two-Phase Binding

Phase 1 (before dialog): Bind minimal runtime host with registry access only

session->bindRuntimeHostForDialog();  // Only registry, no engine/dataset

Phase 2 (after dialog): Complete binding with engine and dataset

session->setupAndStart(config);  // Full binding as before

Changes

DataSourceSession

• Add bindRuntimeHostForDialog() method for early binding
• Only binds registry pointer; engine/dataset are set later

main_window.cpp

• Call bindRuntimeHostForDialog() before showing the dialog
• Remove config JSON injection approach (cleaner API)

SDK (data_source_plugin_base.hpp)

• listAvailableEncodings() now returns std::vector<std::string> directly
• listAvailableEncodingsJson() returns raw JSON for special cases
• Zero-dependency JSON array parser built into pj_base

Tests

• Updated data_source_library_test.cpp with new test cases

Usage from Plugins

// mqtt_source.cpp
PJ::Status loadConfig(std::string_view config_json) override {
  dialog_.loadConfig(config_json);
  // Runtime host is now available here (Phase 1 binding done)
  dialog_.setAvailableEncodings(runtimeHost().listAvailableEncodings());
  return PJ::okStatus();
}

Related PRs

• PR feat(plugin-registry): add listAvailableEncodings method #27 (merged) — Added listAvailableEncodings() to vtable
• pj-official-plugins PR feat(sdk): early runtime host binding for dialog + listAvailableEncodings vector helper #28 — MQTT uses dynamic encodings
• pj-official-plugins PR fix(protoapp): always call loadConfig for streaming sources #29 — ZMQ uses dynamic encodings