Add type annotations to sympy.logic.inference - #30532

#### References to other Issues or PRs

See #28806

#### Brief description of what is fixed or changed

Adds type annotations to `sympy/logic/inference.py` and `release/authors.py`.
In `inference.py` I annotated `valid`, `pl_true`, its inner `_validate`, and
`entails`, plus a `Model` alias for the assignment dicts `pl_true` passes
around; in `authors.py`, `blue`, `red`, and `get_authors`. I left
`literal_symbol` and `satisfiable` alone — `satisfiable`'s return type varies
with `all_models` and the chosen algorithm, so it needs overloads rather than
one signature, which felt like its own change.

#### Other comments

`pl_true` rebound `expr` and `model` to different types inside the body, which
mypy rejects. Rather than widen the parameter types, I gave the intermediates
new names — `sexpr` for the sympified expression, `deep_model` for the atoms
dict — so the parameters keep the types in their signature. No behaviour
change, but it's the one spot where the diff is more than added annotations.

While typing the return I noticed `pl_true` isn't consistent about boolean
results: an input already in `(True, False)` comes back as-is via `return
expr`, while a result that reduces after `subs` goes through `bool(result)`.
Because `BooleanTrue` compares equal to `True`, `pl_true(true)` returns
`BooleanTrue` but `pl_true(x, {x: True})` returns a Python `bool`. I typed the
return as `Boolean | bool | None` to cover both. Would you rather narrow it to
`bool | None` and convert in the first branch, or is the current behaviour
depended on somewhere?

#### AI Generation Disclosure

Claude Code (Claude Opus 5), run in VSCode against a local clone.

sympy/logic/inference.py — AI-generated: the annotations on valid, entails,
pl_true and _validate; the Model alias and TYPE_CHECKING block; and the
pl_true body changes (sexpr, deep_model, and the cast on subs).

release/authors.py — AI-generated: the annotations on blue, red and
get_authors, and the added __future__ import.

I reviewed every line. mypy sympy reports no errors across 1553 files,
ruff check sympy passes, sympy/logic/tests gives 136 passed, and
bin/doctest sympy/logic/inference.py and bin/test quality both pass.


#### Release Notes

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NO ENTRY

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