[Feature request] gcov format version 2 support

[fangsong-cellink]

GCC 14 bumped its gcov intermediate JSON schema to "format_version": "2". And using grcov together with it generates this error:

[ERROR] Format version 2 is not expected, please file a bug on https://github.com/mozilla/grcov

This is triggered in src/parser.rs:

if gcov.format_version != "1" {
    error!(
        "Format version {} is not expected, please file a bug on https://github.com/mozilla/grcov",
        gcov.format_version
    );
}

Currently grcov still generates coverage report which seems to be correct despite of this error message. But I am not very sure whether the best fix is to remove this check directly.

Reproduction (has a dockerfile so we have gcc14 environment):

grcov-gcc14-repro.tar.gz