x.json2: fix tests for deprecated function fast_raw_decode

[lcheylus]

x.json2: fast_raw_decode deprecated after 2025-03-18 => needs to be replaced by decode[json.Any] instead

Fix tests in vlib/x/json2/tests/json2_test.v and vlib/x/json2/decoder2/tests/json2_tests/json2_test.v

Tests OK on Linux Debian/testing (amd64) with prod mode

• Before this fix

$ ./v -prod test vlib/x/json2/tests/json2_test.v
---- Testing... ----------------------------------------------------------------------------------------------------------------------------
 FAIL     0.000 ms vlib/x/json2/tests/json2_test.v
>> compilation failed:
vlib/x/json2/tests/json2_test.v:19:12: error: function `x.json2.fast_raw_decode` has been deprecated since 2025-03-18, it will be an error after 2025-09-14; use `decode[json.Any]` instead
   17 | fn test_fast_raw_decode() {
   18 |     s := '{"name":"Peter","age":28,"salary":95000.5,"title":2}'
   19 |     o := json.fast_raw_decode(s) or {
      |               ~~~~~~~~~~~~~~~~~~
   20 |         assert false
   21 |         json.Any('')

--------------------------------------------------------------------------------------------------------------------------------------------
To reproduce just failure 1 run:    '/home/fox/dev/vlang.git/v' -prod '/home/fox/dev/vlang.git/vlib/x/json2/tests/json2_test.v'
Summary for all V _test.v files: 1 failed, 1 total. Elapsed time: 1067 ms, on 1 job. Comptime: 979 ms. Runtime: 0 ms.

• After fix

$ ./v -prod test vlib/x/json2/tests/json2_test.v
---- Testing... ----------------------------------------------------------------------------------------------------------------------------
 OK       1.709 ms vlib/x/json2/tests/json2_test.v
--------------------------------------------------------------------------------------------------------------------------------------------
Summary for all V _test.v files: 1 passed, 1 total. Elapsed time: 7063 ms, on 1 job. Comptime: 7060 ms. Runtime: 1 ms.

[huly-for-github]

Connected to Huly®: V_0.6-22895

[enghitalo]

I love you! Thank you!

[enghitalo]

I think you can erase the fast_raw_decode function as well

[spytheman]

The current deprecation policy, is to remove functions 6 months after the deprecation date (see doc/docs.md):

// You can also specify a date, after which the function will be
// considered deprecated. Before that date, calls to the function
// will be compiler notices - you will see them, but the compilation
// is not affected. After that date, calls will become warnings,
// so ordinary compiling will still work, but compiling with -prod
// will not (all warnings are treated like errors with -prod).
// 6 months after the deprecation date, calls will be hard
// compiler errors.

i.e. we can remove fast_raw_decode in September

[spytheman]

btw, @lcheylus you can use v -W test . instead of v -prod test . (the later takes much longer) to find other instances of recent warnings, that have not been yet changed.
Thank you for doing this work 🙇🏻‍♂️ .