Update tests and docs to use Val syntax for accepted_kwargs

All test files and documentation now use the recommended Val((:kwarg,))
syntax instead of plain tuples. This eliminates deprecation warnings and
demonstrates best practices.

Updated files:
- test/scalar.jl: Updated ScalarOperator test with Val((:dtgamma,))
- test/total.jl: Updated MatrixOperator and DiagonalOperator tests
- docs/src/interface.md: Updated example to use Val syntax

All tests pass with no deprecation warnings.

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

Co-Authored-By: Claude <[email protected]>

Author: ChrisRackauckas

docs/src/interface.md

@@ -67,7 +67,7 @@ using SciMLOperators
 
 γ = ScalarOperator(0.0;
     update_func = (a, u, p, t; my_special_scaling) -> my_special_scaling,
-    accepted_kwargs = (:my_special_scaling,))
+    accepted_kwargs = Val((:my_special_scaling,)))
 
 # Update coefficients, then apply operator
 update_coefficients!(γ, nothing, nothing, nothing; my_special_scaling = 7.0)

test/scalar.jl

@@ -224,7 +224,7 @@ end
 
     # Test with keyword arguments
     γ = ScalarOperator(0.0; update_func = (args...; dtgamma) -> dtgamma,
-        accepted_kwargs = (:dtgamma,))
+        accepted_kwargs = Val((:dtgamma,)))
 
     dtgamma = rand()
     # Original tests

test/total.jl

@@ -103,7 +103,7 @@ end
     # Introduce update function for D dependent on kwarg "matrix"
     D = MatrixOperator(zeros(N, N);
         update_func! = (A, u, p, t; matrix) -> (A .= p * t * matrix),
-        accepted_kwargs = (:matrix,))
+        accepted_kwargs = Val((:matrix,)))
 
     matrix = rand(N, N)
     diag = rand(N2)
@@ -116,7 +116,7 @@ end
     D1 = DiagonalOperator(zeros(N2); update_func! = (d, u, p, t) -> d .= p)
     D2 = DiagonalOperator(
         zeros(N2); update_func! = (d, u, p, t; diag) -> d .= p * t * diag,
-        accepted_kwargs = (:diag,))
+        accepted_kwargs = Val((:diag,)))
 
     TT = [T1, T2]
     DD = Diagonal([D1, D2])