Add pinyin_group and lazy_pinyin_group functions for grouped pinyin output with apostrophe handling

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Successfully implemented pinyin grouping functions with two variants for different use cases:

New Functions

1. pinyin_group() and lazy_pinyin_group()

• pinyin_group: Returns pinyin as a list (supports multi-pronunciation with heteronym=True)
• lazy_pinyin_group: Returns pinyin as a string (single pronunciation only, simpler output)

Both functions:

• Segment input text and group by words
• Each group returns hanzi and corresponding pinyin
• Handle erhua (儿化音) - combine 儿 with previous character
• Handle apostrophe separation for ambiguous pinyin (e.g., xi'an)
• Support both unicode string AND string list as input
  • String input: performs segmentation
  • List input: skips segmentation (allows custom segmentation)

Implementation Details

Architecture (following existing patterns)

• Added Pinyin.pinyin_group() and Pinyin.lazy_pinyin_group() methods in the Pinyin class
• Module-level functions call the respective methods
• Follows the same pattern as pinyin() / lazy_pinyin() functions

Key Differences

pinyin_group:

[{'hanzi': '你好', 'pinyin': ['ni hao']}]  # pinyin is a list

lazy_pinyin_group:

[{'hanzi': '你好', 'pinyin': 'ni hao'}]  # pinyin is a string

Use Cases

• pinyin_group: When you need multi-pronunciation support or consistency with other functions
• lazy_pinyin_group: Simpler output for common cases where single pronunciation is sufficient
• HTML <ruby> tag integration for annotating Chinese text
• Handling erhua and apostrophe display requirements
• Educational applications with grouped pinyin display

Testing

• All existing tests pass (229 passed, 2 skipped)
• Added 22 comprehensive tests covering both functions
  • Basic functionality, punctuation handling
  • Erhua and apostrophe handling
  • List input support
  • Method existence verification
  • Comparison tests between the two variants

Exports

Both functions are exported from pypinyin/__init__.py:

• pinyin_group
• lazy_pinyin_group

Type hints added to .pyi files for both functions and methods.

Closes #245

Original prompt

---

This section details on the original issue you should resolve

<issue_title>新增一个函数用于实现对结果进行分组输出</issue_title>
<issue_description>## 问题描述

新增一个函数用于实现对结果进行分组（按词语分组、儿化音分组、隔音符号连接的拼音分组）输出:

>>> xxx('你好吗？')
[
   {
      "hanzi": "你好",
      "pinyin": ["ní hǎo"],
   },
   {
      "hanzi": "吗",
      "pinyin": ["ma"],
   },
  {
      "hanzi": "？",
      "pinyin": [],
   },
]

>>> xxx('西安')
[
   {
      "hanzi": "西安",
      "pinyin": ["xi'an"],
   },
]

>>> xxx('花儿')
[
   {
      "hanzi": "花儿",
      "pinyin": ["huar"],
   },
]

case：

• 配合 <ruby> 标签实现汉字标注拼音的显示效果：你好 (níhǎo)吗(ma)？ （当然，这个场景下获取拼音的需求更推荐使用 javascript 库在前端实现）

• 解决儿化音以及类似 xi'an 这种连在一起的拼音的显示场景的需求

#245
</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #280

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