Improve `Display` of `Decimal` values

[neilconway]

Is your feature request related to a problem or challenge?

Decimal values are displayed (e.g., in EXPLAIN or schemas in CLI query results) like Decimal128(Some(20),2,1). The Some seems unnecessary and makes the display hard to read.

Describe the solution you'd like

No response

Describe alternatives you've considered

No response

Additional context

No response

[neilconway]

take