Add ExplicitImports.jl tests for import hygiene

- Add ExplicitImports and Test to test dependencies in Project.toml
- Add tests to verify no implicit imports or stale explicit imports

The package was already clean with no implicit or stale imports.
These tests ensure import hygiene is maintained going forward.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: ChrisRackauckas

Project.toml

@@ -21,3 +21,10 @@ NonlinearProblemLibrary = "0.1"
 ODEProblemLibrary = "1"
 SDEProblemLibrary = "1"
 julia = "1.10"
+
+[extras]
+ExplicitImports = "7d51a73a-1435-4ff3-83d9-f097790105c7"
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+
+[targets]
+test = ["ExplicitImports", "Test"]

test/runtests.jl

@@ -1,2 +1,9 @@
 # The test is simply that all of the examples build!
 using DiffEqProblemLibrary
+using ExplicitImports
+using Test
+
+@testset "ExplicitImports" begin
+    @test check_no_implicit_imports(DiffEqProblemLibrary) === nothing
+    @test check_no_stale_explicit_imports(DiffEqProblemLibrary) === nothing
+end