feat: convert timeout flag to support time formats (e.g., 5s, 100ms)

[soonghee2]

What does this PR do?

• Converts the timeout flag to use flagSet.DurationVar to support time formats (e.g., 5s, 500ms).
• Maintains backward compatibility for integer inputs as milliseconds.
• Applies a default timeout of 100ms for invalid inputs.

Why is this needed?

• This enhancement improves flexibility for users by allowing them to specify timeouts in a more intuitive way.

Related Issue

• Closes timeout flag from int to DurationVar #1321

detailed

Change the Option.timeout variable type to time.Duration.
Declare a new Option.StrTimeout field as a string to receive the timeout option in string format.
If the string represents an integer, interpret it as milliseconds (as before).
If the string is in formats like 3s or 1m, parse it directly as a time.Duration with time.ParseDuration.

[GeorginaReeder]

Thanks for your contribution @soonghee2 ! :)