Enable FunctionProperties rendered docs QA

[ChrisRackauckas-Claude]

Ignore this PR until reviewed by @ChrisRackauckas.

Summary

• Enable SciMLTesting rendered public API docs QA for FunctionProperties.
• No source, docs, or behavior changes. The exported API already has source docstrings and explicit rendered @docs entries in docs/src/api.md.
• This is separate from the unrelated docs cleanup workflow PR Fix docs cleanup shell quoting #71.

Local validation

• git diff --check passed.
• QA passed with SciMLTesting v2.2.0: Quality Assurance | 18 pass, 18 total.
• Docs build completed with include("docs/make.jl"); note the docs config already has pre-existing warnonly entries, and local deployment was skipped.
• Pkg.test() passed: Core/core_tests.jl 272/272.
• Runic v1.7.0 passed over src, test, and docs.