Enforce 1000 queued-logs hard cap in LogsBatcher

The logs buffering spec requires SDKs to enforce a hard limit of 1000 queued logs and to send no more than 100 logs per envelope (see [develop docs](https://develop.sentry.dev/sdk/telemetry/logs/#buffering)).

In [`sentry-core/src/logs.rs`](https://github.com/getsentry/sentry-rust/blob/5975043daabe826b31ce293629298f10d8e2cb7b/sentry-core/src/logs.rs), `LogsBatcher` already flushes at 100 logs per envelope but currently does not enforce a 1000-item queue cap. We should add this cap so logs above the limit are dropped instead of allowing unbounded queue growth.