Add org_id and strict_trace_continuation client options

[szokeasaurusrex]

Add the Rust SDK configuration options required by the strict trace continuation spec: org_id and strict_trace_continuation. This task should expose the public API and resolve the SDK organization ID, but should not parse incoming baggage or enforce strict trace continuation yet. This is part of #1016 and replaces #1162 with a narrower, behavior-neutral API task.

Add API docs on the new fields and a CHANGELOG.md entry because this is a public API addition.

Implementation notes

Target files:

• sentry-core/src/clientoptions.rs
• CHANGELOG.md

Implementation:

• Add pub org_id: Option<OrganizationId> to ClientOptions.
• Add pub strict_trace_continuation: bool to ClientOptions.
• Set defaults:
  • org_id: None
  • strict_trace_continuation: false
• Include both fields in ClientOptions debug output.
• Add an internal helper such as pub(crate) fn resolved_org_id(&self) -> Option<OrganizationId>.
• Resolve the SDK organization ID by preferring explicit org_id, then self.dsn.as_ref().and_then(Dsn::org_id).
• Document that org_id is mainly needed for self-hosted Sentry and local Relay setups.
• Do not parse incoming baggage in this task.
• Do not enforce the strict continuation decision in this task.
• Do not create head-of-trace DSC in this task.

Tests:

• Explicit org_id takes precedence over the DSN-derived organization ID.
• DSN-derived organization ID is used when explicit org_id is absent.
• Missing or unparsable DSN organization ID returns None.
• Defaults are org_id: None and strict_trace_continuation: false.
• Validate with cargo test -p sentry-core clientoptions.

[linear-code]

RUST-251