Improve explicit imports hygiene

This PR ensures SciMLDocs follows best practices for explicit imports:

1. Fixed implicit imports in docs/make.jl:
   - Explicitly import makedocs, deploydocs, MathJax3, HTML from Documenter
   - Changed Documenter.HTML to HTML (now explicitly imported)

2. Fixed implicit imports in docs/make_aggregate.jl:
   - Split comma-separated imports into separate lines
   - Explicitly import HTML from Documenter
   - Fixed incorrect Docs.HTML reference (should be Documenter.HTML)

3. Added ExplicitImports tests:
   - Added ExplicitImports to test dependencies in Project.toml
   - Created test checking for implicit and stale imports in test/runtests.jl

The main package (src/SciMLDocs.jl) is an empty module with no imports, which is correct.
All changes maintain backward compatibility while improving code clarity.

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

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

Author: claude

Project.toml

@@ -9,7 +9,8 @@ version = "1.7.0"
 julia = "1.10"
 
 [extras]
+ExplicitImports = "7d51a73a-1435-4ff3-83d9-f097790105c7"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["Test"]
+test = ["ExplicitImports", "Test"]

docs/make.jl

@@ -1,4 +1,4 @@
-using Documenter
+using Documenter: Documenter, makedocs, deploydocs, MathJax3, HTML
 
 cp("./docs/Manifest.toml", "./docs/src/assets/Manifest.toml", force = true)
 cp("./docs/Project.toml", "./docs/src/assets/Project.toml", force = true)
@@ -41,7 +41,7 @@ makedocs(
         "http://www.scholarpedia.org/article/Differential-algebraic_equations",
         "https://computing.llnl.gov/projects/sundials",
     ],
-    format = Documenter.HTML(
+    format = HTML(
         assets = ["assets/favicon.ico"],
         canonical = "https://docs.sciml.ai/stable/",
         mathengine = mathengine

docs/make_aggregate.jl

@@ -1,4 +1,6 @@
-using Documenter, LibGit2, Pkg
+using Documenter: Documenter, HTML
+using LibGit2
+using Pkg
 using MultiDocumenter
 
 include("CommercialSupportComponent.jl")
@@ -255,7 +257,7 @@ MultiDocumenter.make(
     ),
     custom_scripts = [
         "https://www.googletagmanager.com/gtag/js?id=G-Q3FE4BYYHQ",
-        Docs.HTML(
+        HTML(
             """
             window.dataLayer = window.dataLayer || [];
             function gtag(){dataLayer.push(arguments);}

test/runtests.jl

@@ -1 +1,8 @@
 using Test
+using ExplicitImports
+using SciMLDocs
+
+@testset "ExplicitImports" begin
+    @test check_no_implicit_imports(SciMLDocs) === nothing
+    @test check_no_stale_explicit_imports(SciMLDocs) === nothing
+end