Fix LIST/UIDL streaming parsing and reject zero message numbers

[Boomboomdunce]

Summary

• preserve the expected POP3 response shape from Request through PopStream so LIST and UIDL parsing no longer guesses from partial buffered bytes
• reject invalid LIST/UIDL message numbers of 0 in both single-line and multi-line parser paths
• add chunked-stream regression tests for split multi-line responses plus parser tests for illegal zero message numbers

Root Cause

PopStream previously queued only a bare Command, so the parser could not tell whether LIST or UIDL had been issued with an argument. In streaming reads, that meant a partial multi-line response like +OK 1 120\r\n could be accepted as a valid single-line reply before the remaining lines arrived.

Separately, the parser accepted 0 as a valid POP3 message number in LIST and UIDL responses even though POP3 message numbers are 1-based.

This PR fixes both issues by preserving a ResponseShape derived from the original Request for the streaming path and by tightening LIST/UIDL message-number validation.

Test Plan

• cargo test split_list_without_argument_still_parses_as_multiline
• cargo test split_uidl_without_argument_still_parses_as_multiline
• cargo test response::parser::test::test_list
• cargo test response::parser::test::test_uidl
• cargo test response::parser::test::test_list_rejects_zero_message_number
• cargo test response::parser::test::test_uidl_rejects_zero_message_number
• cargo test response::parser::
• cargo test dele_marks_message_as_deleted_locally
• cargo test --no-default-features --features runtime-tokio stream::tests::poll_next_returns_connection_closed_on_eof
• cargo test --no-default-features --features runtime-tokio stream::tests::buffer_accepts_messages_larger_than_twenty_megabytes
• cargo test (fails only because the existing E2E tests require SERVER, PORT, USERNAME, and PASSWORD in the environment)