Scan Delete Support Part 5: Positional Delete Parsing

[sdd]

Continues the series of scan delete file support PRs.

Builds on top of #982: click 5504434 to see just the changes that are unique to this PR rather than the preceding ones.

• Adds parsing of positional delete files to the DeleteFileManager
• Updates the integration tests in crates/integration_tests/tests/shared_tests/read_positional_deletes.rs to include a working end-to-end test that processes positional deletes
• Refactors scan.rs and arrow/reader.rs so that when delete file support is specified as being disabled, and a delete file is encountered, the error is returned from the read phase rather than the plan phase.

Issue: #630