Closes #393
Closes #392

Enables fig.colorbar() to use both ax (positioning) and span/rows/cols (extent) parameters together. Previously, span was ignored when ax was provided.

Examples

# Bottom colorbar spanning only columns 1-2
fig, axs = uplt.subplots(nrows=2, ncols=3)
fig.colorbar(cm, ax=axs[0, :], span=(1, 2), loc="bottom")

# Right colorbar spanning only rows 1-2
fig, axs = uplt.subplots(nrows=3, ncols=2)
fig.colorbar(cm, ax=axs[:, 0], rows=(1, 2), loc="right")

Notes

• Use span= or cols= for horizontal colorbars (top/bottom)
• Use rows= for vertical colorbars (left/right)
• Validation errors/warnings guide correct parameter usage
• Array behavior preserved: fig.colorbar(cm, ax=axs[:]) still works
• Added 15 tests to test_colorbar.py
• Fully backward compatible