DECIMAL regex in csv reader does not accept positive exponent specifier

[jdcasale]

Describe the bug

Decimals in scientific notation are frequently expressed with an (admittedly unnecessary) positive exponent specifier, e.g "3.106e+04". The existing regex allows for negative exponent specifiers, but does not recognize a number with a positive specifier. This causes the parser to infer the type of any column with positive exponent specifiers as a Utf8 instead of float.

As a sanity check, I tried the same thing in DuckDB, and their csv parser does not make this error.

To Reproduce

Either attempt to infer schema for a csv file containing the offending pattern (like I have done here in this provided example) or just run the existing regex directly against the example offender: "3.106e+04", it will not match.

Expected behavior

The decimal regex recognizes "3.106e+04" as a float value, not a Utf8 string.

Additional context

[tustvold]

It is worth noting that we only supported parsing scientific notation as of this morning - #5611

[tustvold]

label_issue.py automatically added labels {'arrow'} from #5649