Add int16 support to PACK/UNPACK

[andresovela]

PACK/UNPACK should support int16_t for int16x8 quantized models

[github-actions]

"This issue is being marked as stale due to inactivity. Remove label or comment to prevent closure in 5 days."

[andresovela]

#2737 is still open

[github-actions]

"This issue is being marked as stale due to inactivity. Remove label or comment to prevent closure in 5 days."

[andresovela]

#2737 is still open

[github-actions]

"This issue is being marked as stale due to inactivity. Remove label or comment to prevent closure in 5 days."

[andresovela]

#2737 is still open

[github-actions]

"This issue is being marked as stale due to inactivity. Remove label or comment to prevent closure in 5 days."