inspector: refactor to rename and comment methods

@eugeneo What do you think? Its "cosmetic" in some ways, but the renaming helped me understand the code better. I've a couple open questions, I'll comment on my own PR to point them out.

Pure refactor, makes no functional changes but the renaming helped me see more clearly what the relationship was between methods and variables.

• Renamed methods to reduce number of slightly different names for the same thing ("thread" vs "io thread", etc.).
• Annotated many local functions as static.
• Added comments where it was useful to me.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)