[lee3Q]

convert_min_size multiplied the parsed number by the unit without an overflow check, and silently ignored numbers that do not fit in usize.

• dust -z 99999999T panics in debug builds ("attempt to multiply with overflow") and wraps silently in release builds, so the filter ends up with a wrong size.
• dust -z 18446744073709551616 was dropped with no message, unlike other invalid values.

This uses checked_mul and treats any value that can't be represented like the other invalid values: it prints Ignoring invalid min-size: <input> and the option is ignored.

Behavior changes to be aware of:

• Numbers above usize::MAX now print the existing "Ignoring invalid min-size" warning instead of being dropped silently.
• On 32-bit targets a T suffix value used to become Some(0) without a warning; it now gives None with the warning.

Testing: on x86_64 debug, the config unit tests pass (37), and the new assertions fail on the base commit and pass with this change. The integration tests have 4 failures that are identical with and without this change. I did not run 32-bit binaries (only a 32-bit cargo check --tests), and I did not get a fully green full test run.