feat(toolbox): Filter Editor toolbox plugin

PJ3's 'Apply filter to data' as a PJ4 toolbox panel: multi-curve source
selection, closed predefined-transform catalogue, live preview, optional
alias, copy/paste clipboard. Launches from the plot right-click via the
manifest plot_action tag.

Strategy pattern across the plugin / SDK boundary:
  - Contract (plotjuggler_sdk#120 pj_plugins/filter_protocol/):
    abstract PJ::sdk::FilterTransform + FilterTransformFactory.
  - Strategies (this plugin, builtin_transforms.hpp): 12 concrete classes
    deriving from PJ::sdk::FilterTransform.
  - Registration: registerAllTransforms() at loaderInit.

Tests (builtin_transforms_test.cpp): per-transform deterministic-causal
+ bit-identity. Pure C++ gtest, no Qt.

Bumps extern/plotjuggler_core submodule to the contract+tags commit
(plotjuggler_sdk#120).

Author: pabloinigoblasco

CMakeLists.txt

@@ -46,6 +46,7 @@ if(TARGET plotjuggler_sdk::plugin_sdk)
   add_subdirectory(toolbox_colormap)
   add_subdirectory(toolbox_quaternion)
   add_subdirectory(toolbox_reactive_scripts_editor)
+  add_subdirectory(toolbox_filter_editor)
   add_subdirectory(toolbox_mosaico)
   return()
 endif()
@@ -151,5 +152,6 @@ else()
   add_subdirectory(toolbox_fft)
   add_subdirectory(toolbox_colormap)
   add_subdirectory(toolbox_quaternion)
+  add_subdirectory(toolbox_filter_editor)
   add_subdirectory(toolbox_mosaico)
 endif()

extern/plotjuggler_core

@@ -0,0 +1,48 @@
+find_package(nlohmann_json REQUIRED)
+
+include(${CMAKE_CURRENT_LIST_DIR}/../cmake/EmbedManifest.cmake)
+include(${CMAKE_CURRENT_LIST_DIR}/../cmake/EmbedUi.cmake)
+
+add_library(toolbox_filter_editor_plugin SHARED filter_editor_plugin.cpp)
+target_compile_features(toolbox_filter_editor_plugin PRIVATE cxx_std_20)
+target_compile_options(toolbox_filter_editor_plugin PRIVATE ${PJ_WARNING_FLAGS})
+
+target_link_libraries(toolbox_filter_editor_plugin PRIVATE
+  plotjuggler_sdk::plugin_sdk
+  nlohmann_json::nlohmann_json
+  ${CMAKE_DL_LIBS}
+)
+
+pj_embed_manifest(toolbox_filter_editor_plugin
+  HEADER   ${CMAKE_CURRENT_BINARY_DIR}/generated/filter_editor_manifest.hpp
+  VAR_NAME kFilterEditorManifest
+)
+
+pj_embed_ui(toolbox_filter_editor_plugin
+  UI_FILE  ${CMAKE_CURRENT_SOURCE_DIR}/filter_editor_dialog.ui
+  HEADER   ${CMAKE_CURRENT_BINARY_DIR}/generated/filter_editor_dialog_ui.hpp
+  VAR_NAME kFilterEditorDialogUi
+)
+
+# v4 plugin discovery: emit a sidecar .pjmanifest.json the host can scan
+# pre-dlopen. Content derived from manifest.json + {abi_major, family}.
+pj_emit_plugin_manifest(toolbox_filter_editor_plugin
+  FAMILY        toolbox
+  MANIFEST_FILE ${CMAKE_CURRENT_SOURCE_DIR}/manifest.json
+)
+
+# Built-in predefined transforms catalogue lives in this plugin (it provides
+# them); the SDK contract they implement is in plotjuggler_sdk::plugin_sdk.
+# Tests guard the per-transform PJ3-mirror math + the SDK contract (the
+# default appendTail loops calculateNextPoint, save/load round-trips).
+if(TARGET GTest::gtest_main)
+  add_executable(builtin_transforms_test builtin_transforms_test.cpp)
+  target_compile_features(builtin_transforms_test PRIVATE cxx_std_20)
+  target_compile_options(builtin_transforms_test PRIVATE ${PJ_WARNING_FLAGS})
+  target_link_libraries(builtin_transforms_test PRIVATE
+    plotjuggler_sdk::plugin_sdk
+    nlohmann_json::nlohmann_json
+    GTest::gtest_main
+  )
+  add_test(NAME builtin_transforms_test COMMAND builtin_transforms_test)
+endif()