Improve Returns section formatting in lu function

Replace bold asterisk formatting with plain descriptive text in Returns
section:
- "**(If permute_l is False)**" → "When permute_l is False, the function returns:"
- "**(If permute_l is True)**" → "When permute_l is True, the function returns:"

Also add missing period to parameter description in lu_solve.

This follows NumPy/SciPy documentation conventions for clearer, more
readable docstrings.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: antonwolfy

dpnp/scipy/linalg/_decomp_lu.py

@@ -95,7 +95,7 @@ def lu(
 
     Returns
     -------
-    **(If ``permute_l`` is ``False``)**
+    When ``permute_l`` is ``False``, the function returns:
 
     p : (..., M, M) dpnp.ndarray or (..., M) dpnp.ndarray
         If `p_indices` is ``False`` (default), the permutation matrix.
@@ -110,7 +110,7 @@ def lu(
     u : (..., K, N) dpnp.ndarray
         Upper triangular or trapezoidal matrix.
 
-    **(If ``permute_l`` is ``True``)**
+    When ``permute_l`` is ``True``, the function returns:
 
     pl : (..., M, K) dpnp.ndarray
         Permuted ``L`` matrix: ``pl = P @ L``.
@@ -273,7 +273,7 @@ def lu_solve(lu_and_piv, b, trans=0, overwrite_b=False, check_finite=True):
     lu, piv : {tuple of dpnp.ndarrays or usm_ndarrays}
         LU factorization of matrix `a` (..., M, M) together with pivot indices.
     b : {(M,), (..., M, K)} {dpnp.ndarray, usm_ndarray}
-        Right-hand side
+        Right-hand side.
     trans : {0, 1, 2} , optional
         Type of system to solve: