chore: remove serde as direct dependency

[jiacai2050]

Which issue does this PR close?

Closes #

Rationale for this change

Clean unused dep

What changes are included in this PR?

Remove direct dependency on serde

 (main)$ cargo tree -i serde
serde v1.0.152
├── mysql v23.0.1
│   └── sqlness v0.4.3 (/Users/jiacai/code/misc/sqlness/sqlness)
│       └── sqlness-cli v0.4.3 (/Users/jiacai/code/misc/sqlness/sqlness-cli)
├── mysql_common v0.29.2
│   └── mysql v23.0.1 (*)
├── rust_decimal v1.28.1
│   └── mysql_common v0.29.2 (*)
├── serde_json v1.0.93
│   ├── mysql v23.0.1 (*)
│   └── mysql_common v0.29.2 (*)
└── toml v0.5.11
    └── sqlness v0.4.3 (/Users/jiacai/code/misc/sqlness/sqlness) (*)

Are there any user-facing changes?

No

How does this change test

CI

[waynexia]

great 👍