style: unify identifier naming per updated conventions

Automated with clang-tidy readability-identifier-naming (config added to
.clang-tidy) plus scripted passes, per the updated rules now documented
in CONTRIBUTING.md:

- types (class/struct/enum/alias/template params): PascalCase
- functions, variables, members: snake_case (incl. rational -> Rational)
- private/protected members: trailing underscore; static member
  variables likewise (instance_, available_themes_)
- constants and enum values: snake_case (kLinear -> k_linear,
  F32P -> f32p); ALL_CAPS reserved for macros
- macros: OAK_ prefix (OLIVE_ADD_TEST/OLIVE_ASSERT/OLIVE_CONFIG ->
  OAK_ADD_TEST/OAK_ASSERT/OAK_CONFIG, GL_PREAMBLE -> OAK_GL_PREAMBLE,
  include guards -> OAK_*)
- file names: all lowercase (Current/Plugin/OliveHost/OliveClip/
  OlivePluginInstance -> current/plugin/olivehost/oliveclip/
  oliveplugininstance)
- getters share the member name sans underscore, setters set_foo()
- Qt and third-party (OpenFX) virtual overrides and framework callbacks
  keep their original names (exempt in .clang-tidy)

Manual follow-ups required where automation could not reach:
- string-based QMetaObject/SIGNAL/SLOT references updated to renamed
  methods (AddTask, CreatedFile, DeleteSpecificFile, moveSelectionUp, ...)
- macro bodies referencing renamed methods (OLIVE_CONFIG,
  NODE_DEFAULT_DESTRUCTOR, MANAGEDDISPLAYWIDGET_*)
- self-shadowing locals renamed where signals/methods became same-named
  (size_changed, worker_count, selected_items, import param, filters)
- third_party OFX member/namespace usages restored (OFX::Host::*,
  _created, _clipPrefsDirty, createInstance, clearPersistentMessage)
- STL protocol aliases restored (const_iterator) with .clang-tidy
  ignore rules; qHash overloads restored

Full build and test suite pass: ctest 4/4, ~1960 gtest cases green.

app/task/project/loadotio/loadotio.cpp

@@ -221,17 +221,17 @@ bool LoadOTIOTask::Run()
 
 				track->AppendBlock(block);
 
-				rational start_time;
-				rational duration;
+				Rational start_time;
+				Rational duration;
 
 				if (otio_block->schema_name() == "Clip" ||
 					otio_block->schema_name() == "Gap") {
-					start_time = rational::fromDouble(
+					start_time = Rational::fromDouble(
 						static_cast<OTIO::Item *>(otio_block)
 							->source_range()
 							->start_time()
 							.to_seconds());
-					duration = rational::fromDouble(
+					duration = Rational::fromDouble(
 						static_cast<OTIO::Item *>(otio_block)
 							->source_range()
 							->duration()
@@ -262,9 +262,9 @@ bool LoadOTIOTask::Run()
 
 					// Set how far the transition eats into the previous clip
 					transition_block->set_offsets_and_length(
-						rational::fromRationalTime(
+						Rational::fromRationalTime(
 							otio_block_transition->in_offset()),
-						rational::fromRationalTime(
+						Rational::fromRationalTime(
 							otio_block_transition->out_offset()));
 
 					if (previous_block) {