Clarify multiple IV curve requirement for Sandia fitting methods

[anshurajbisoyi98-ctrl]

Both fitting-function docstrings describe per-curve arrays but do not explicitly say that multiple IV curves are required. This adds that requirement to their introductory descriptions and clarifies that each curve needs corresponding effective irradiance and cell temperature data.

Validation: 11 tests passed in the De Soto and PVsyst test modules (including both Sandia fitting tests). HTML documentation built with gallery execution disabled, and both rendered function pages were checked. The tests emit numerical/deprecation warnings; the documentation emits an existing configuration-cache warning.

• Closes Clarify docstrings for ivtools.sdm.fit_pvsyst_sandia, .fit_desoto_sandia #1715
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[cwhanse]

The need to include effective irradiance and cell temperature is clear with ee and tc in the ivcurves dict.

[cwhanse]

Suggested change

	and cell temperature conditions. Each curve must have corresponding
	effective irradiance and cell temperature data in ``ivcurves``.
	and cell temperature conditions.

[anshurajbisoyi98-ctrl]

Thanks for the suggestion. I removed the redundant sentence from both docstrings in commit d0c2a5e.

[cwhanse]

Suggested change

	and cell temperature conditions. Each curve must have corresponding
	effective irradiance and cell temperature data in ``ivcurves``.
	and cell temperature conditions.

[anshurajbisoyi98-ctrl]

Thanks for the suggestion. I removed the redundant sentence from both docstrings in commit d0c2a5e.