test(sdk): add comprehensive unit tests for all SDKs
Adds unit tests covering tensor operations, type enums, client
functionality, and serialization for all 12 SDK implementations:
- JavaScript (Vitest): tensor, types, client tests
- Python (pytest): tensor, types, client tests
- Go: standard library tests with httptest
- Flutter (flutter_test): tensor, types tests
- Java (JUnit 5): tensor, types tests
- Rust: embedded module tests
- Ruby (minitest): tensor, types tests
- C# (xUnit): tensor, types tests
Tests cover:
- Tensor creation (zeros, ones, random, randn, eye, arange, linspace)
- Tensor operations (reshape, transpose, indexing)
- Reductions (sum, mean, std, min, max)
- Activations (relu, sigmoid, softmax)
- Serialization/deserialization
- Type enums and configuration
- Client request building
- Error handling
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