[dmxlol]

Which issue does this PR close?

Closes #8430.

Rationale for this change

A metadata-only change, such as setting a file's mtime after upload, currently costs a full
read and rewrite. OpenDAL's copy cannot carry new metadata, and it refuses from == to.
S3 can make this change with one zero-body CopyObject that sends
x-amz-metadata-directive: REPLACE. The issue has the details.

What changes are included in this PR?

• CopyOptions gets user_metadata and content_type, named as in WriteOptions and
  ComposeOptions. copy_with and copier_with get matching builder methods, and
  OpCopy gets matching getters.
• New capability flags copy_with_user_metadata and copy_with_content_type.
  CorrectnessCheckLayer returns Unsupported when a service does not advertise them.
• Operator::copy* accepts from == to when either option is set.
• services-s3:
  • CopyObject sends x-amz-metadata-directive: REPLACE, Content-Type and
    x-amz-meta-*.
  • A multipart copy sets the same headers on CreateMultipartUpload.
  • Both capability flags are advertised.
• Tests:
  • an OpCopy options round trip
  • a correctness-check test: Unsupported without the capability, and same-path copy
    allowed only with metadata
  • two S3 request-shape tests on the existing mock transport: single and multipart copy
  • a behavior test, test_copy_with_user_metadata_in_place, gated on
    copy_with_user_metadata

Tested against:

• AWS S3 (eu-central-1, a fresh unversioned bucket): the copy behavior tests pass 19 of 21,
  including the new one. The two failures, test_copy_with_source_version_*, fail the same
  way on main against the same bucket ("must have version") because the bucket has no
  versioning. A same-key copy_with with user metadata, content type and a source length
  hint sent one request and kept the ETag; the metadata changed and the content did not.
• Silo (the fixtures/s3 image): full s3 behavior suite, 128 of 128.
• Garage v2.1.0: 115 of 128; the same 13 fail on main (conditional writes, response
  overrides, special characters), none of them copy.

Are there any user-facing changes?

Yes. This PR adds two options, two builder methods and two capability flags; nothing
existing changes. The behavior is documented on CopyOptions::user_metadata: when either
option is set, the destination does not inherit source metadata, and unset fields such as
Cache-Control take the service default.

Breaking changes

AI Usage Statement

• Harness: Claude Code, a coordinator session that delegated to a subagent.
• Model: Claude Opus 5.5 (claude-opus-5-5).
• Effort: default.
• Role: Drafted the change, the tests and this description under human direction. A human
  reviewed the change and submits it.
• Assumptions and unknowns:
  • Testing used AWS S3, Silo and Garage, as listed above.
  • Not checked: S3 Express One Zone, R2, Neon and the other providers in
    compatible_services.md. All of them are advertised with the new flags.

🤖 Generated with Claude Code