Improve performance for large bodies more

[LucasPickering]

Description

Describe the change. If there is an associated issue, please include the issue link (e.g. "Closes #xxx"). For UI changes, please also include screenshots.

• Disable formatting/highlighting on bodies large than the "large" body size threshold (1MB by default, but it's configurable)
• Run body parsing in a background task

Known Risks

What issues could potentially go wrong with this change? Is it a breaking change? What have you done to mitigate any potential risks?

• large bodies still result in pretty poor UI performance while visible on the screen, it's just not nearly as bad as it used to be
• Lack of prettyification/highlighting might be confusing. I didn't want to spend screen real estate on a message, so supplement with a red indicator on the response size, plus some documentation

QA

How did you test this?

manually in UI

Checklist

• Have you read CONTRIBUTING.md already?
• Did you update CHANGELOG.md?
  • Only user-facing changes belong in the changelog. Internal changes such as refactors should only be included if they'll impact users, e.g. via performance improvement.
• Did you remove all TODOs?
  • If there are unresolved issues, please open a follow-on issue and link to it in a comment so future work can be tracked