`parse_decimal` allows invalid inputs `e5` and `-`

[neilconway]

Describe the bug

See repro.

To Reproduce

use arrow_array::types::Decimal128Type;
use arrow_cast::parse::parse_decimal;

parse_decimal::<Decimal128Type>("0E5", 10, 2);  // Ok(0)
parse_decimal::<Decimal128Type>("e5", 10, 2);   // Ok(0)
parse_decimal::<Decimal128Type>("-.", 10, 2);   // Ok(0)

Expected behavior

Invalid inputs should be rejected with an error.

Additional context

No response

[neilconway]

take