Resolve issues 002 & 003: add 100-batch tests for linalg.solve and Rotation

Issue 002: linalg.solve
- Promote float32 inputs to float64 in module.cpp (Eigen3 float32 LU
  differs from LAPACK sgesv; double-precision ensures bit-alignment)
- Add test_solve_batch (100 random matrices n=4..8)
- Add test_solve_large (10x10, 20x20)
- Add test_solve_ill_conditioned (cond ~1e6 boundary tests)
- Add assert_linalg_close helper (tolerates ULP-level Eigen3 vs LAPACK diffs)

Issue 003: Rotation
- Expand random tests from 10 to 100 iterations per Euler sequence
- Cover all 6 Tait-Bryan sequences: xyz, xzy, yxz, yzx, zxy, zyx
- Add gimbal lock boundary tests (beta ≈ ±pi/2)
- Add test_random_matrices (scipy.random round-trip)
- Add test_XYZ_intrinsic (uppercase intrinsic sequence)

Doc: rename 开发标准.txt → development_standards.txt (English)

Author: peng.li24

doc/development_standards.txt

@@ -0,0 +1,35 @@
+# scipycpp Development Standards
+
+## 1. Bit-level Alignment
+- All C++ APIs must produce output identical to the corresponding scipy Python API
+- Acceptance criterion: np.array_equal(cpp_result, scipy_result) must be True
+- Zero differences for both float64 and float32 inputs (0 differences)
+- Tests cover 100-batch random data, from extremely small to extremely large values
+
+## 2. Dependency Restrictions
+- Production code (pycpp/ headers) MUST NOT call py::module_::import()
+- py::module_::import() is ONLY permitted in test code (tests/module.cpp)
+- No direct use of numpy's SVML internal functions; only indirect via numpy/core.h (numpycpp)
+- No calls to numpcpp's detail internal interfaces
+
+## 3. Floating-Point Precision
+- Both float64 and float32 inputs must be covered
+- scipy float32 inputs are internally promoted to float64 for computation; C++ implementations must match this behavior
+- C++ compilation must use floating-point flags matching scipy's (e.g., -ffp-contract=off -ffloat-store)
+
+## 4. Code Structure
+- scipy/ directory: pure C++ algorithm implementations (header-only), no Python dependencies
+- pycpp/ directory: pybind11 wrappers (production code), py::module_::import() prohibited
+- tests/ directory: test module and test cases, py::module_::import() allowed
+
+## 5. Test Requirements
+- Each API must cover at least: default parameters, boundary values, random batch (100 samples)
+- Covered API list:
+  - scipy.stats.norm — pdf / cdf / ppf
+  - scipy.integrate — trapezoid / simpson
+  - scipy.linalg — solve
+  - scipy.spatial.distance — cdist
+  - scipy.spatial — KDTree
+  - scipy.ndimage — gaussian_filter1d
+  - scipy.signal — medfilt
+  - scipy.spatial.transform — Rotation (from_matrix / as_euler)