ref(core): Use profile ID constant from conventions (#24976)

Uses `SENTRY_PROFILE_ID` from `@sentry/conventions/attributes`.
Deprecates the existing core constant while preserving its public export
and identical `sentry.profile_id` key; emitted values and
span/transaction serialization remain unchanged.

Part of #24961 / [JS-3868](https://linear.app/getsentry/issue/JS-3868).

Co-authored-by: GPT-6 <codex@openai.com>