common: fix --override-kv to support comma-separated values (#18056)

common: fix --override-kv to support comma-separated values (#18056)

* common: fix --override-kv to support comma-separated values

* Update common/arg.cpp

Co-authored-by: Xuan-Son Nguyen <redacted>
* common: deprecate repeated arguments, suggest comma-separated values

* common: add comma escape support for --override-kv

* common: optimize duplicate detection with insert().second

Co-authored-by: personalmountains <redacted>
* common: migrate all repeated args to comma-separated syntax

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Co-authored-by: Xuan-Son Nguyen <redacted>
Co-authored-by: personalmountains <redacted>