SAVI formula divides by (1+L) instead of multiplying

[brendancol]

Describe the bug

The SAVI implementation has the (1+L) factor on the wrong side of the division. The standard formula from Huete (1988) is:

SAVI = ((NIR - Red) / (NIR + Red + L)) * (1 + L)

The code computes:

(NIR - Red) / ((NIR + Red + L) * (1 + L))

This puts (1+L) in the denominator instead of the numerator. With the default L=0.5, every SAVI result is too small by a factor of (1+L)^2 = 2.25.

Both _savi_cpu (line 1065) and _savi_gpu (line 1080) have the same bug.

Separately, the EBBI GPU kernel uses nb.int64(10) where the CPU version uses plain 10. Minor type inconsistency worth fixing at the same time.

Expected behavior

For NIR=0.8, Red=0.2, L=0.5:

• Correct: ((0.8 - 0.2) / (0.8 + 0.2 + 0.5)) * 1.5 = 0.6 / 1.5 * 1.5 = 0.6
• Current code: 0.6 / (1.5 * 1.5) = 0.6 / 2.25 = 0.267

Affected code

• xrspatial/multispectral.py line 1065: denominator = soma * (1.0 + soil_factor)
• xrspatial/multispectral.py line 1080: denominator = soma * (nb.float32(1.0) + soil_factor)
• xrspatial/multispectral.py line 1370: nb.int64(10) type inconsistency in EBBI