Add basic unit tests for TMath::Sqrt and TMath::Log in MathCore

[Sachet-debug]

What does this PR do?

This pull request adds a new GoogleTest-based unit test file test_basic_math.cxx inside math/mathcore/test/.

Purpose of the PR

MathCore already contains many statistical and numerical tests, but it did not have a simple beginner-friendly test covering basic TMath functionality.
This PR introduces very small but meaningful tests for:

• TMath::Sqrt
• TMath::Log

These tests validate correctness for simple inputs (e.g., Sqrt(9) → 3, Log(e) → 1).

Why this is useful

• Helps expand MathCore test coverage.
• Provides a simple reference test for newcomers who want to understand the GoogleTest structure in ROOT.
• Ensures basic TMath behavior is validated in CI across compilers/platforms.

What is included

• New file: test_basic_math.cxx
• CMake registration using ROOT_ADD_GTEST

Tests included

TEST(MathCoreTest, SqrtFunction) {
    double out = TMath::Sqrt(9.0);
    EXPECT_NEAR(out, 3.0, 1e-12);
}

TEST(MathCoreTest, LogFunction) {
    double out = TMath::Log(2.71828182845904523536);
    EXPECT_NEAR(out, 1.0, 1e-12);
}