Fix undefined behavior for infinite array indices

[MAXDVVV]

Fixes #3533.

This avoids undefined behavior when array indices are non-finite numbers.

Changes:

• treat non-finite numeric array keys as missing for has()
• ignore non-finite numeric array keys for del()
• clamp finite numeric indices before converting them to int
• add regression coverage for has(infinite) and del(.[infinite])

Validation:

• git diff --check