Add basic Sendable correctness, update to SQLite 3.43.1

[gwynne]

Changes in this release:

• We now satisfy StrictConcurrency=complete with no warnings in this package.
• We also now satisfy ExistentialAny.
• Update embedded SQLite from 3.43.0 to 3.43.1 (SQLite release notes)
• The vendoring script is now an SPM command plugin. Run it with swift package --disable-sandbox vendor-sqlite. Accepts --help, --verbose, and --force options. (Users should not need to run this command.)
• The SQLCustomFunction feature's API documentation has been heavily improved.
• The package now requires Swift 5.7, in alignment with Vapor.
• The options used when compiling the SQLite sources have been adjusted to better match current recommendations and usage.
• The generated source files (the vendored libsqlite3) have been renamed for consistency.

[gwynne]

API breakage failure is spurious. Dependents check failure is fixed by vapor/sqlite-kit#105.

[codecov-commenter]

Codecov Report

Merging #51 (6086f3f) into main (0a33df1) will not change coverage. The diff coverage is 74.07%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #51 +/- ## ======================================= Coverage 66.36% 66.36% ======================================= Files 8 8 Lines 669 669 ======================================= Hits 444 444 Misses 225 225 ``` | [Files Changed](https://app.codecov.io/gh/vapor/sqlite-nio/pull/51?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor) | Coverage Δ | | |---|---|---| | [Sources/SQLiteNIO/SQLiteData.swift](https://app.codecov.io/gh/vapor/sqlite-nio/pull/51?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxpdGVOSU8vU1FMaXRlRGF0YS5zd2lmdA==) | `81.92% <0.00%> (ø)` | | | [Sources/SQLiteNIO/SQLiteDataType.swift](https://app.codecov.io/gh/vapor/sqlite-nio/pull/51?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxpdGVOSU8vU1FMaXRlRGF0YVR5cGUuc3dpZnQ=) | `0.00% <0.00%> (ø)` | | | [Sources/SQLiteNIO/SQLiteError.swift](https://app.codecov.io/gh/vapor/sqlite-nio/pull/51?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxpdGVOSU8vU1FMaXRlRXJyb3Iuc3dpZnQ=) | `26.81% <ø> (ø)` | | | [Sources/SQLiteNIO/SQLiteRow.swift](https://app.codecov.io/gh/vapor/sqlite-nio/pull/51?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxpdGVOSU8vU1FMaXRlUm93LnN3aWZ0) | `92.85% <ø> (ø)` | | | [Sources/SQLiteNIO/SQLiteConnection.swift](https://app.codecov.io/gh/vapor/sqlite-nio/pull/51?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxpdGVOSU8vU1FMaXRlQ29ubmVjdGlvbi5zd2lmdA==) | `65.97% <76.47%> (ø)` | | | [Sources/SQLiteNIO/SQLiteCustomFunction.swift](https://app.codecov.io/gh/vapor/sqlite-nio/pull/51?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxpdGVOSU8vU1FMaXRlQ3VzdG9tRnVuY3Rpb24uc3dpZnQ=) | `83.67% <85.71%> (ø)` | | | [Sources/SQLiteNIO/SQLiteStatement.swift](https://app.codecov.io/gh/vapor/sqlite-nio/pull/51?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxpdGVOSU8vU1FMaXRlU3RhdGVtZW50LnN3aWZ0) | `89.58% <100.00%> (ø)` | |

[penny-for-vapor[bot]]

These changes are now available in 1.7.0