ScriptPipelineState progress quality of life changes

[mgi388]

First off, thanks for doing this! Using this has fixed the flakiness I was experiencing with the script not always being ready.

1. When reading the docs for progress() it says:

returns a number between 0 and 100.0 to represent the current script pipeline progress,

But that seems odd to me. A value of 100.0 means "100 percent loaded" but that is a UI concern. If anything, I feel this should return progress as a float between 0.0 and 1.0.

2. num_loaded_scripts() should arguably be named loaded_script_count() and num_processing_scripts() -> processing_script_count(). See my argument/rationale from an issue in Bevy: Add num_entities() to World bevyengine/bevy#19780 (comment). It's not an objective choice, but take a look anyway.

3. processing_batch_completed() should arguably be named is_processing_batch_completed(). You can follow breadcrumbs here Rename Timer::paused to Timer::is_paused and Timer::finished to Timer::is_finished bevyengine/bevy#19110 but tl;dr; is that most Rust functions seem to use this format.

4. Thinking about progress() and my comments in 1., I wonder if you should actually just remove it entirely. Users can already get all the data by calling num_loaded_scripts() and num_processing_scripts() and I personally wouldn't ever need to know the percent progress: just whether or not it's done. That is, it really feels more like a UI concern. Up to you though!

5. Regarding the use of the term batch in processing_batch_completed(), what is the purpose? As a user, I don't feel like I really know anything about batches here so it was confusing to me looking at this method name and wondering if it's what I want. If it was just processing_completed() (read: is_processing_completed()), would that lose any information?