Make integer_subbyte Fully Compliant with is_integral

[osayamenja]

Context

See #1631

Change

Adds integral type trait for integer_subbyte

[osayamenja]

@thakkarV Closing the loop on #1631, let me know if this is not actually needed and I will close this instead.

[thakkarV]

@ccecka for review too

[osayamenja]

If needed, I can also register float8 and half for is_floating_point

[github-actions[bot]]

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[github-actions[bot]]

This PR has been labeled inactive-90d due to no recent activity in the past 90 days. Please close this PR if it is no longer required. Otherwise, please respond with a comment indicating any updates.