ref: move user_consent to sentry_run_t for thread-safe access

[jpnurmi]

Extracted from #1542.

Moves require_user_consent and user_consent from sentry_options_t to sentry_run_t as atomic longs, and adds two helpers:

• sentry__run_should_skip_upload() — lock-free consent check callable from any thread via the refcounted run pointer, replacing the raw long*-into-options pattern.
• sentry__run_load_user_consent() — loads <database>/user-consent into the run via atomic store, so callers outside the options lock can refresh consent while worker threads read it.

The batcher is updated to use the new helper; no other call sites are introduced yet.

Why

Unblocks #1542 and #1649, which need consent reads from worker threads and consent refreshes from contexts without the global options (e.g. the native crash daemon).

Scope

Pure refactor — no behavioral changes. No new consent checks, no daemon changes, sentry__capture_envelope signature unchanged.

#skip-changelog (internal refactor)

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