Export InvPreconditioner

[ChrisRackauckas-Claude]

What changed and why

InvPreconditioner already has a docstring and rendered manual entries, but it is not exported and therefore is not public API. Export it so downstream packages can use the inverse-preconditioner wrapper without reaching into LinearSolve internals. This unblocks the requested cleanup in SciML/OrdinaryDiffEq.jl#4391 (comment).

This public API addition should be included in a LinearSolve 5.15.0 or later minor release. The version is not changed here because LinearSolve performs version bumps in dedicated release PRs.

Ignore this PR until it has been reviewed by @ChrisRackauckas.

Failing before / passing after

On exact parent 50563b88, the focused public-API assertion failed:

$ julia +1.11 --project -e 'using LinearSolve, Test; @test Base.isexported(LinearSolve, :InvPreconditioner)'
Test Failed at none:1
  Expression: Base.isexported(LinearSolve, :InvPreconditioner)

ERROR: There was an error during testing

With this change, the same command exits 0. It also exits 0 on Julia 1.10.11.
The two-line committed assertion was removed by @ChrisRackauckas during review at #1272 (comment); the commands above are the retained fail-before/pass-after evidence.

Verification

Julia 1.11.9:

$ GROUP=Core julia +1.11 --project -e 'using Pkg; Pkg.test()'
Test Summary:              | Pass  Total  Time
SpecializingFactorizations |   18     18  3.7s
Testing LinearSolve tests passed

$ GROUP=QA julia +1.11 --project -e 'using Pkg; Pkg.test()'
Test Summary:     | Pass  Total     Time
Quality Assurance |   50     50  6m24.1s
Testing LinearSolve tests passed

$ JULIA_DEPOT_PATH=<clean-isolated-depot> julia +1.11 --project=docs docs/make.jl
[ Info: CheckDocument: running document checks.
[ Info: RenderDocument: rendering document.
# exit 0

$ julia +1.12 -m Runic --check src/LinearSolve.jl test/Core/basictests.jl
# exit 0

$ typos src/LinearSolve.jl test/Core/basictests.jl
# exit 0

$ git diff --check
# exit 0

The isolated depot was necessary because this host's global CondaPkg Pixi cache contains zero-byte Python files left by the 2026-08-22 disk-full incident. Clean upstream/main and this branch both build the docs successfully with the isolated depot; this is local cache corruption, not a repository failure.

Not verified

GPU-specific groups and optional solver backend groups were not run locally. No dependency is added or changed.

🤖 Generated with Codex CLI 0.151.0 (model: gpt-5.6-sol; session: local session ID 01a04fab-48db-7e03-9f47-20c69464527f)