Overhaul "free budget" and migrate non-metered code

[jayz22]

What

Resolves #1061

• Overhaul the "free budget":

  • Add two fields internal_limit and internal_total_count to budget dimension for keeping track of internal work being done, which don't get metered for fee, but need to be limited for DOS prevention.
  • Remove the with_free_budget interface and replace it with with_internal_mode (and a with_debug_budget on the host side that wraps around it and asserts host is in DEBUG mode), taking two closures and ensuring 1. the internal_limit is not exceeded 2. any error occurring within is suppressed. The error suppression part is to prevent error-based logic existing outside the closure that accidentally causes divergences between debug and no-debug workflows.
  • Adds a new hostile contract case for testing.

• A refactoring to split the budget.rs into multiple smaller files. The file was getting big (1200+ lines) and hard to navigate.

• Migrate all existing non-metered code to metered version, this includes diagnostic logging, diagnostic event, auth preflight code.

Why

[TODO: Why this change is being made. Include any context required to understand the why.]

Known limitations

[TODO or N/A]

[jayz22]

As I was writing some test, I realize most of the currently diagnostic code are unmetered. I will fix the metering on them. Marked as draft.

[jayz22]

All diagnostic workflows have been converted to metered code. Marking this back to ready for review.

[graydon]

Looking good! Handful of changes requested but I think this is fairly close to what we should be merging, thanks!