Ensuring consistency in support for the Timestamp data type format in different statements.

**Describe the feature you'd like**

Currently, there is inconsistency in the support for the Timestamp data type format across statements such as insert, select, and load data infile. Furthermore, the documentation lacks comprehensive descriptions in this regard.
Some test cases and examples: https://qiok3h8ob4.feishu.cn/docx/P1LBdzVIeoPSuHxUUBBcgGq9n7c?from=from_copylink

**Desired Improvements**

1. Support for String Format Timestamps
Implement support for Timestamps in string format, including parsing, validation, and support for millisecond-level precision. The expected format is: yyyy-MM-dd HH:mm:ss.SS.

2. Support for int64 Format Timestamps
Extend support to include Timestamps in int64 format.

3. Conversion Support with timestamp Function
Allow conversion between string/int64 format Timestamps using the timestamp function.

4. Consistent Behavior for Timestamp Columns with Indexes
Ensure uniform behavior when dealing with Timestamp columns that have indexes.

By implementing these improvements, we aim to enhance consistency and usability across various statements and operations involving Timestamp data types.

The issue describes inconsistencies in timestamp format support across insert, select, and load data infile statements. Start by examining the SQL parser and execution engine code for timestamp handling. Look for existing timestamp parsing and validation logic. The linked test cases document provides specific examples to understand the current behavior and desired improvements.

索引モデルが issue の本文から書いたものです。