fix: improve JSON tag handling and validation logic to support omitzero

[yockii]

1. to support new tag omitzero for go 1.24+
2. fix some tags in json like json:"id,omitempty,string"
3. fix null filed in json string, when the field is not required, and it is "null" value, the validation may failed.
4. add test for these situations.

eg:

type User struct { ID uint64 `json:"id,omitempty,string"` Name string `json:"name"` Age int `json:"age,omitzero"` Addr Address `json:"address,omitempty"` } type Address struct { Zip string `json:"zip"` } 

and with json:

{ "name": "Yockii", "address": null } 

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.59%. Comparing base (8e5611c) to head (ba2ee13).

Additional details and impacted files

@@ Coverage Diff @@ ## master #1076 +/- ## ======================================= Coverage 99.59% 99.59% ======================================= Files 34 34 Lines 2206 2216 +10 ======================================= + Hits 2197 2207 +10  Misses 6 6 Partials 3 3 

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