[SEDONA-753] feat: add eo:cloud_cover and eo:snow_cover STAC extensions to reader

[prantogg]

Did you read the Contributor Guide?

• Yes, I have read the Contributor Rules and Contributor Development Guide

Is this PR related to a ticket?

• Yes, and the PR name follows the format [SEDONA-XXX] my subject.

What changes were proposed in this PR?

• Adds eo:cloud_cover and eo:snow_cover STAC extension fields (from the EO extension) to the STAC reader output schema when present in the source data. These are promoted as top-level DoubleType columns alongside the existing grid:code extension field.

How was this patch tested?

• Extended existing extension test to filter on eo:cloud_cover and eo:snow_cover values from the local test STAC collection
• Updated schema validation test to include the new extension fields

Did this PR include necessary documentation updates?

• No, this PR does not affect any public API so no need to change the documentation.