Declare documented API public (for downstream ExplicitImports)

[ChrisRackauckas-Claude]

Motivation

ForwardDiff currently exports only DiffResults and does not declare any names public. As a result, downstream packages that access the documented API in qualified form — e.g. ForwardDiff.jacobian, ForwardDiff.gradient, ForwardDiff.GradientConfig — get flagged by ExplicitImports.jl's check_all_qualified_accesses_are_public, because to that tool every one of these reads as "non-public" (not exported, not declared public), even though the documentation presents them as the public API.

Many SciML packages (and others) run ExplicitImports as part of their QA suite, so each currently has to carry a manual ignore-list entry for ForwardDiff names. Declaring the documented surface public lets that boilerplate go away and makes the package's public/internal boundary explicit to tooling.

What this does

Adds a single Expr(:public, ...) declaration near the end of src/ForwardDiff.jl covering the names that are documented as the public API:

• Core entry points (in the @docs blocks of docs/src/user/api.md): derivative, derivative!, gradient, gradient!, jacobian, jacobian!, hessian, hessian!
• Config types (also @docs in api.md): DerivativeConfig, GradientConfig, JacobianConfig, HessianConfig
• User-facing types/accessors documented in the user guides: Chunk (Configuring Chunk Size), Dual (Custom tags), value (Retrieving Lower-Order Results), and can_dual (has a ForwardDiff.can_dual docstring and is referenced as a user-extensible hook in the cannot-dual error message)

Exports are unchanged — this only marks names public, it does not bring anything into downstream scope unqualified.

public was added in Julia 1.11, so the declaration is @static-guarded (VERSION >= v"1.11.0-DEV.469"); Julia 1.10 is completely unaffected (the block is simply not evaluated there).

Deliberately not included

I left out names that appear only in the internals/implementation doc (docs/src/dev/how_it_works.md) and are not presented to users as public API: Partials, partials, npartials, and Tag. If maintainers consider any of these part of the supported surface, I'm happy to add them.

Note

This is a draft / proposal for maintainer consideration — please feel free to adjust the exact set of names. Marked draft and should be ignored until reviewed by @ChrisRackauckas.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.74%. Comparing base (090ddbb) to head (b11acb5).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #819   +/-   ##
=======================================
  Coverage   90.74%   90.74%           
=======================================
  Files          11       11           
  Lines        1070     1070           
=======================================
  Hits          971      971           
  Misses         99       99           

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[mcabbott]

Xref #744, in which there are various suggestions for what to mark public, none exactly agreeing with the list here.