feat: Enable read only transaction support

[p0isonra1n]

This should fix issue #98 but I am not sure the best way to test it.

[haaawk]

I think we need the transaction to make sure that it never writes if it's marked as read only. That probably requires examining every statement it receives and throwing exception when write is received.

[haaawk]

There's no BEGIN READONLY syntax in sqlite/libsql -> https://www.sqlite.org/lang_transaction.html

> sqlite3 ~/test.db
SQLite version 3.43.2 2023-10-10 13:08:14
Enter ".help" for usage hints.
sqlite> BEGIN READONLY;
Parse error: near "READONLY": syntax error
  BEGIN READONLY;
        ^--- error here

[haaawk]

I guess we could try do this for remote only code considering tursodatabase/libsql@91f4780

[haaawk]

I guess we could try do this for remote only code considering tursodatabase/libsql@91f4780

but it seems to work only with embedded replicas which this client does not support

[haaawk]

I tested this with turso db shell and it seems that read only transactions don't work for hrana:

→  select * from test;
A 
→  begin readonly; insert into test values(101); select * from test; commit;
A   
101

[haaawk]

I'm closing this for now @p0isonra1n but feel free to reopen if you still want to work on this.