support jackson-core fast number parsing

Jackson 2.14's JsonFactory supports these features.

• StreamReadFeature.USE_FAST_DOUBLE_PARSER
• StreamWriteFeature.USE_FAST_DOUBLE_WRITER

play-json's BigDecimalParser may also benefit from using jackson-core's BigDecimalParser - you should keep the number length check that play-json has but the parsing of the string can benefit from jackson-core's BigDecimalParser which has special code to speed up parsing of very long numbers.

Just thought I'd raise awareness of these features of jackson-core. With the StreamReadFeature and StreamWriteFeature, you would probably want to make those opt-in - that play-json should probably not use them by default.

Jackson 2.15.0-rc1 is out today (Mar 18, 2023). It has an additional feature - StreamReadFeature.USE_FAST_BIG_NUMBER_PARSER

• v2.15.0 also has a StreamReadConstraints with some defaults that might cause issues in some edge cases

You can make the limits effectively unlimited by creating a JsonFactory that overrides the default StreamReadConstraints.
An example that increases the max number len:

   val jsonFactory = JsonFactory.builder()
     .streamReadConstraints(StreamReadConstraints.builder().maxNumberLength(Integer.MAX_INTEGER).build())
     .build()

If you do plan to upgrade to use Jackson 2.15, you will need to consider how to integrate Jackson's StreamReadConstraints (particularly the number len check) with play-json's pre-existing support for checking the len of BigDecimal/BigInteger.

Start by locating play-json's BigDecimalParser and its Jackson JsonFactory integration, then review Jackson's USE_FAST_DOUBLE_PARSER, USE_FAST_DOUBLE_WRITER, USE_FAST_BIG_NUMBER_PARSER, and StreamReadConstraints. Done means assessing opt-in fast parsing and writing while preserving play-json's existing number-length checks and accounting for Jackson 2.15 constraints.