BITCOUNT Upper bound calculation fix

[vazois]

This PR fixes issue #1135

[Copilot]

Pull Request Overview

This PR addresses issue #1135 by fixing the BITCOUNT upper bound calculation.

• Updated the BITCOUNT calculation logic to ensure the end offset is inclusive
• Added a test case that validates using int.MaxValue as the upper bound

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
test/Garnet.test/GarnetBitmapTests.cs	Added a test to verify BITCOUNT with an inclusive upper bound
libs/server/Resp/Bitmap/BitmapManagerBitCount.cs	Adjusted upper bound calculation to account for an inclusive index

Comments suppressed due to low confidence (2)

libs/server/Resp/Bitmap/BitmapManagerBitCount.cs:73

• The change to 'valLen - 1' ensures the end offset is treated as an inclusive index; please verify that this adjustment consistently meets the intended BITCOUNT behavior across all edge cases.

endOffset = endOffset >= valLen ? valLen - 1 : endOffset;

test/Garnet.test/GarnetBitmapTests.cs:2317

• [nitpick] Consider adding additional test cases covering boundary scenarios, such as negative offsets, to further validate the BITCOUNT logic.

count = db.StringBitCount(key, 0, int.MaxValue);