Reduce Miri CI runtime by ignoring tests over 60 seconds

### Is your feature request related to a problem or challenge?

Follow-up to #10803. The latest Miri run on main took 24m and reported 19 tests exceeding nextest’s 60-second slow-test threshold.

### Describe the solution you'd like

Mark those tests with #[cfg_attr(miri, ignore)] while preserving their normal cargo test coverage.

### Describe alternatives you've considered

_No response_

### Additional context

see https://github.com/apache/arrow-rs/pull/10803#issuecomment-5463002763 for more context

Review the context from #10803 and its linked pull-request comment, then run the Miri tests with nextest to identify the 19 tests exceeding the 60-second threshold. Add #[cfg_attr(miri, ignore)] to those tests while preserving normal cargo test coverage; done means the Miri run no longer reports those slow tests and regular tests still run.

Written by the indexing model from the issue text.