Improve explicit imports hygiene

[ChrisRackauckas-Claude]

Summary

This PR improves the package's explicit imports hygiene by:

• Making Random imports explicit (Random, AbstractRNG, randexp) instead of relying on using Random which imports all exports
• Adding ExplicitImports.jl to test dependencies
• Adding ExplicitImports tests to the qa.jl test suite

Changes Made

src/PoissonRandom.jl:3

Changed from:

using Random

to:

using Random: Random, AbstractRNG, randexp

This explicitly lists what is imported from Random, preventing reliance on implicit/transitive imports.

Project.toml

• Added ExplicitImports to [extras] section
• Added ExplicitImports to test targets
• Added compat entry for ExplicitImports = "1.14.0"

test/qa.jl

• Added using ExplicitImports
• Added new @testset "ExplicitImports" with tests:
  • check_no_implicit_imports(PoissonRandom) - ensures no implicit imports
  • check_no_stale_explicit_imports(PoissonRandom) - ensures no unused imports

Test Results

All tests pass, including the new ExplicitImports tests:

• ✓ Aqua (10 tests)
• ✓ JET static analysis (6 tests)
• ✓ ExplicitImports (2 tests)
• ✓ All Poisson sampling tests

Benefits

1. Clear dependencies: Makes it explicit what is imported from each module
2. Prevents transitive dependency issues: Won't accidentally rely on exports that come transitively through dependencies
3. Better maintainability: Clear what the code actually uses
4. Enforced in CI: ExplicitImports tests prevent regression

cc: @ChrisRackauckas

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