Potential arithmetic overflow in Generator#nextAuctionLengthMs()

```

long numEventsForAuctions =
(config.configuration.numInFlightAuctions * GeneratorConfig.PROPORTION_DENOMINATOR)

/ GeneratorConfig.AUCTION_PROPORTION;

```

The multiplication is done on 32-bit integers while long is expected (numEventsForAuctions).

There is possibility for arithmetic overflow

Imported from Jira [BEAM-2805](https://issues.apache.org/jira/browse/BEAM-2805). Original Jira may contain additional context.
Reported by: yuzhihong@gmail.com.

Start by locating Generator#nextAuctionLengthMs() and inspect the arithmetic involving numInFlightAuctions, PROPORTION_DENOMINATOR, and AUCTION_PROPORTION. Confirm the multiplication is evaluated without 32-bit overflow, then check relevant existing tests or add coverage demonstrating correct behavior for large values.

Written by the indexing model from the issue text.