ALL：fixing static analysis warnings

[felixYyu]

this PR fixed these grouping parentheses are unnecessary. cc @rdblue @RussellSpitzer

iceberg\core\src\main\java\org\apache\iceberg\BaseFileScanTask.java:224: [UnnecessaryParentheses] These grouping parentheses are unnecessary; it is unlikely the code will be misinterpreted without them
          (this.file().equals(other.file())) &&
          ^
    (see https://errorprone.info/bugpattern/UnnecessaryParentheses)
  Did you mean 'this.file().equals(other.file()) &&'?

• Core：Removing an initialization that sets a variable to null #4429
• Core：Removing a fully defined type that is already imported #4430
• Static Analysis: Supressions we know are false positive #4437
• Static Analysis: Rewrite empty and inappropriate Javadocs #4438
• Static Analysis: Missing private constructor, method need return single mutable, and other few static warning #4439
• Static Analysis: Changing the access modifiers on all the JDBC Static Values #4440
• Static Analysis: Lambda should be a method reference #4442
• Core: Avoid Date for timestamp to string conversion #4444

[felixYyu]

please review again，thanks @RussellSpitzer

[RussellSpitzer]

Most of these look fine, I would if possible (and I know I asked to group these together) separate out the changes which make semantic changes to the code into their own PR's.

For example

"Removing an initialization that sets a variable to null" Good, keep here doesn't actually change anything
"Removing a fully defined type that is already imported" good keep here
"Supressions we know are false positive" Keep here
"Removing empty java docs, fixing java docs" Keep here
"Changing parens" Keep here

--

"Changes an iterator to a list" Separate PR
"Changing the access modifiers on all the JDBC Static Values" Separate PR
"Changes in date handling classes" Separate PR

[felixYyu]

I will separate out the changes which make semantic changes to the code into their own PR's.

[felixYyu]

The task was not fully completed，It will be finished today. @RussellSpitzer