Support read-only databases

[simolus3]

This adds a readOnly option supported by open and openAsync (both on the web and on native platforms):

• On the web, enabling that option passes flags: 'r' to the constructor. Otherwise, we pass c (for create, write, read; the default).
• On native platforms, this passes a readOnly flag along to sqlite3_open_v2, where we use the same logic to determine flags to include.

I have tested these changes on an iOS simulator, I didn't look into web tests.

Closes #421.

[ospfranco]

You need to modify all interfaces, including the libsql ones.

There was a github macOS runner migration, please re-merge main into your branch, should fix the xcode-select error in the sqlcipher test run.

[simolus3]

You need to modify all interfaces, including the libsql ones.

Unfortunately, it looks like libsql only supports passing database flags from Rust. The C bindings op-sqlite depends on don't seem to provide flags that could open read-only databases.

I have changed the implementation to throw in this case, and updated the test.

[ospfranco]

android turso build fails

[simolus3]

Can you cancel the old iOS run from the previous commit? I think it'll just timeout