Add getDSPClock() method and ChannelGroup class

[AleMax]

For a personal project of mine I needed the getDSPClock() function on a ChannelControl in FMOD's core API.
In my use case I had to get this from an EventInstance.getChannelGroup(), which returns a ChannelGroup which inherits ChannelControl's methods.

For this I added a ChannelGroup Class in the core/ subdirectory, which implements only the getDSPClock function that I needed. Anyone is welcome to implement more functions.
I added the getChannelGroup to FmodEvent, so I can retreive a ChannelGroup.

I made this for myself, but I made the PR if there is interest in merging this upstream just in case.

(I also fixed a spelling error in the documentation, this is unrelated to the rest of the PR, sorry for adding this here too)

[Copilot]

Pull request overview

This PR adds a minimal ChannelGroup wrapper to expose FMOD ChannelControl::getDSPClock()-related functionality to Godot scripts, primarily to support retrieving DSP clock timing from a Studio::EventInstance via EventInstance.getChannelGroup().

Changes:

• Added new core FmodChannelGroup class with get_dsp_clock() and get_parent_dsp_clock() bindings.
• Added FmodEvent.get_channel_group() method and bound it for scripting use.
• Registered the new class in module initialization and fixed a docs typo for the git submodule clone flag.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/studio/fmod_event.h	Exposes get_channel_group() on FmodEvent and includes the new core wrapper.
src/studio/fmod_event.cpp	Binds and implements get_channel_group() to return a FmodChannelGroup wrapper.
src/register_types.cpp	Registers FmodChannelGroup with Godot’s ClassDB.
src/core/fmod_channel_group.h	Introduces FmodChannelGroup wrapper and create_ref() helper.
src/core/fmod_channel_group.cpp	Implements/binds DSP clock accessors.
docs/src/doc/advanced/1-compiling.md	Fixes --recurse-submodules spelling in docs.

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[Copilot]

get_channel_group() currently wraps the returned FMOD::ChannelGroup by always calling FmodChannelGroup::create_ref(channel_group), which (as written) creates a new wrapper each call and overwrites the channel group's userData. To avoid repeated allocations and inconsistent wrapper identity, consider reusing an existing wrapper via channel_group->getUserData() when available.

Suggested change

	if (channel_group) {
	if (channel_group) {
	void* user_data = nullptr;
	ERROR_CHECK_WITH_REASON(channel_group->getUserData(&user_data), vformat("Cannot get ChannelGroup userData"));
	if (user_data) {
	return Ref<FmodChannelGroup>(static_cast<FmodChannelGroup*>(user_data));
	}