fix: apply JSONReader context to SimpleDateFormat values

[DarrenChangJR]

What this PR does and why

The SimpleDateFormat value reader currently invokes
SimpleDateFormat::new. It therefore ignores an explicitly configured
JSONReader.Context locale and zone, reconstructing the formatter with JVM
defaults instead.

This change replaces that generic constructor adapter with a small dedicated
reader. It keeps the existing string wire representation, uses the context
locale when one is configured, and applies the context zone after construction.

Reproducer

With Locale.FRANCE and GMT+08 set on the reader context, deserializing
"MMM" as SimpleDateFormat now produces a formatter whose time-zone ID is
GMT+08:00 and which formats epoch zero as janv.. Previously it produced
Jan in the JVM time zone.

Tests

• text character input;
• UTF-8 byte input;
• JSONB input;
• existing DateFormatTest and AutoTypeFilterTest2 coverage;
• mvn -pl core -DskipTests validate;
• clean full core suite: 7,977 tests, no failures or errors.

Checklist

• Text and JSONB paths retain the existing pattern-string wire form.
• Locale and zone both differ from JVM defaults in the regression.
• Existing JSONB auto-type coverage passes.
• Compatibility facade changes are kept in a separate PR.

中文说明

修改内容和原因

当前 SimpleDateFormat value reader 通过 SimpleDateFormat::new 构造对象，
因此即使调用方在 JSONReader.Context 中明确配置 locale 和时区，重建后的
formatter 仍使用 JVM 默认值。

本修改使用一个小型、无状态的专用 reader，保持原有 pattern 字符串 wire form，
在 locale 存在时用它构造 formatter，并设置 context 时区。

测试

回归测试覆盖字符 JSON、UTF-8 JSON 和 JSONB；已有日期与 JSONB auto-type 测试、
Maven validate，以及 clean 后完整 7,977 个 core 测试均通过。