Improve SessionPoolExample by replacing unbounded fixed thread pool with bounded ThreadPoolExecutor

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/iotdb/issues) and found nothing similar.

### Motivation

I am sometimes frustrated when using the IoTDB CLI because the output of certain commands is difficult to read when the result set is large. The CLI currently prints results in a plain format which may be harder to interpret for users analyzing time-series data interactively.

Improving the CLI output formatting (for example better alignment or optional table-style display) would improve usability, especially for users exploring IoTDB from the command line.

### Solution

One possible solution is to improve the CLI output formatting by introducing a table-style display for query results.

For example, results could be formatted with aligned columns and clearer separators so that timestamps and values are easier to read.

Additionally, an optional CLI flag (for example `--pretty`) could allow users to enable or disable enhanced formatting depending on their preference.

The implementation could be handled in the CLI output handling logic located in:

`iotdb-client/cli/src/main/java/org/apache/iotdb/cli`

### Alternatives

An alternative approach could be to keep the current output format but allow users to export query results directly to formats such as CSV or JSON for easier processing in external tools.

However, improving the CLI display would provide a better interactive experience directly within the terminal.

### Are you willing to submit a PR?

- [x] I'm willing to submit a PR!

Start by locating SessionPoolExample and reconciling the requested thread-pool change with the issue body, which instead discusses CLI output formatting in iotdb-client/cli/src/main/java/org/apache/iotdb/cli. Confirm which scope is intended, then identify the relevant tests or runnable example; done means the selected change is implemented without unbounded thread creation and its behavior is verified.

Written by the indexing model from the issue text.