Fix name conflict with Nemo.integrate

Change `using Nemo` to `import Nemo` in test files to avoid
exporting Nemo's `integrate` function which conflicts with
SymbolicIntegration.integrate

This resolves test failures in CompatHelper PRs #16 and #17 where
the ambiguous `integrate` function caused UndefVarError.

Affected files:
- test/methods/risch/test_complex_fields.jl
- test/methods/risch/test_bronstein_examples.jl
- test/methods/risch/test_algorithm_internals.jl
- test/methods/risch/bronstein_examples.jl

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

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

Author: ChrisRackauckas

test/methods/risch/bronstein_examples.jl

@@ -1,5 +1,5 @@
 using AbstractAlgebra
-using Nemo
+import Nemo
 using SymbolicIntegration
 SI = SymbolicIntegration
 

test/methods/risch/test_algorithm_internals.jl

@@ -2,7 +2,7 @@ using Test
 using SymbolicIntegration
 using Symbolics
 using AbstractAlgebra
-using Nemo
+import Nemo
 
 @testset "[Risch] Algorithm Internals" begin
     # Test internal algorithm components to ensure they work with the new API

test/methods/risch/test_bronstein_examples.jl

@@ -2,7 +2,7 @@ using Test
 using SymbolicIntegration
 using Symbolics
 using AbstractAlgebra
-using Nemo
+import Nemo
 
 @testset "[Risch] Bronstein Algorithm Examples" begin
     # Examples from "Symbolic Integration I: Transcendental Functions" by Manuel Bronstein

test/methods/risch/test_complex_fields.jl

@@ -2,7 +2,7 @@ using Test
 using SymbolicIntegration
 using Symbolics
 using AbstractAlgebra
-using Nemo
+import Nemo
 
 @testset "[Risch] Complex Fields Operations" begin
     # Note: These tests use internal SymbolicIntegration functions