chore(typing): decide ty policy + fix diagnostics for examples/

[jxnl]

examples/ is currently excluded from ty checks; running ty on it reports many diagnostics.

Repro:

• uv sync --all-extras
• uv run ty check examples (currently: Found 138 diagnostics)

Top buckets observed:

• Missing optional deps used only in examples (langsmith, streamlit, nltk, spacy, loguru, erdantic, etc.).
• Examples importing modules that aren’t packaged/importable in that context (e.g. local models, intra-example imports).
• Intentional “wrong type” example calls that need cast(...) or # type: ignore[...] to keep examples runnable while still type-checkable.

Goal

• Decide a policy for examples:
  • Either make uv run ty check examples pass with light annotations/guards, or
  • Keep excluded and add a separate optional CI job for “typed examples” subset.

Possible approach

• Wrap optional imports in try/except ImportError (or if TYPE_CHECKING:) so type checking doesn’t require installing every demo dependency.
• For “demo-only” type violations, add targeted # type: ignore[rule] with justification.
• Consider splitting examples that require heavy deps into a separate folder excluded by default.