Improve ResponseDate parsing

[osadchuk-andrii]

Summary

Enable parsing of additional date formats (including nanosecond precision) in CopyObjectResult.
This makes the minio-java client compatible with SeaweedFS responses.

Problem

Currently, ResponseDate parses only two formats:

"yyyy-MM-dd'T'HH':'mm':'ss'.'SSS'Z'" 
"yyyy-MM-dd'T'HH':'mm':'ss'Z'"

If the date contains nanoseconds, parsing fails with a DateTimeParseException:

io.minio.errors.XmlParserException: java.time.format.DateTimeParseException: Text '2025-08-23T12:22:54.239913137Z' could not be parsed at index 19
	at io.minio.Xml.unmarshal(Xml.java:55)

Example

SeaweedFS response (nanoseconds):

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<CopyObjectResult>
    <LastModified>2025-08-23T11:26:27.109253154Z</LastModified>
    <ETag>03da054f179eed855c27d7d6b2041e2a</ETag>
</CopyObjectResult>

MinIO response (milliseconds):

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<CopyObjectResult xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
    <LastModified>2025-08-23T11:27:44.684Z</LastModified>
    <ETag>"03da054f179eed855c27d7d6b2041e2a"</ETag>
</CopyObjectResult>

Both are valid according to the S3 API spec (LastModified is any string DateTime parsable by strtotime).

Solution

Use ZonedDateTime.parse without a custom formatter.
It falls back to ISO_ZONED_DATE_TIME and supports all previously accepted formats as well as those with nanoseconds.
Additionally, it simplifies the code.

Compatibility

No breaking changes - existing formats continue to be parsed correctly.

[harshavardhana]

Please fix the CI issues @osadchuk-andrii Thank you.

[osadchuk-andrii]

@harshavardhana I’ve run the checks twice in the forked repo, and they all passed: osadchuk-andrii#1
Could we just rerun the checks again?

[balamurugana]

The PR is wrong. Refer https://github.com/minio/minio-java/pull/1621/files#diff-24f6a0826a9c9e3da367f04f6857e6b82a6702315054dda729af415c445df538R59 and wait for v9.0.0