[codex] Add field value codec for collection mapping

[aruis]

Summary

• add a shared field value codec for normal fields, SET, and JSON_SET mapping
• apply field-level conversion to entity criteria compilation while preserving resolver-only behavior
• support string-to-number conversion in the default value converter
• bump project and documentation versions to 3.26.12

Validation

• git diff --check
• ./gradlew :muyun-database-core:test --tests net.ximatai.muyun.database.core.orm.EntityMapperTest --tests net.ximatai.muyun.database.core.orm.CriteriaSqlCompilerTest
• ./gradlew :muyun-database-core:test