sql/pgwire: buffer messages during COPY TO and startup

[rafiss]

fixes #97314
backport fixes #99546

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sql: buffer COPY OUT data

Rather than sending each COPY result row one-by-one, now the data will
get buffered, then flushed when the buffer size limit is reached or when
sending ReadyForQuery.

This fixes an issue that was causing the ruby-pg test to hang, since it assumes
the data will be buffered.

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pgwire: buffer startup messages when creating connection

This avoids sending each ParameterStatus one-by-one.

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sql: refactor CopyIn handling

This makes it so we don't need to manually send a CommandComplete.
Instead, when the CopyInResult is closed, CommandComplete will be sent,
similar to how it works for other message types.

Release note: None

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

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[cockroach-teamcity]

This change is 

[otan]

fancy

[rafiss]

bors r+

[craig]

Build failed (retrying...):

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[craig]

Build failed (retrying...):

• Bazel Essential CI (Cockroach)

[craig]

Build failed (retrying...):

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[craig]

Build succeeded:

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[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

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error setting reviewers, but backport branch blathers/backport-release-23.1-99761 is ready: POST https://api.github.com/repos/cockroachdb/cockroach/pulls/100029/requested_reviewers: 422 Reviews may only be requested from collaborators. One or more of the teams you specified is not a collaborator of the cockroachdb/cockroach repository. []

Backport to branch 23.1.x failed. See errors above.

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[otan]

blathers backport 23.1

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

---

error creating backport branch refs/heads/blathers/backport-release-23.1-99761: POST https://api.github.com/repos/cockroachdb/cockroach/git/refs: 422 Reference already exists []

Backport to branch 23.1 failed. See errors above.

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