Dereference of opaque `sqlite3_context` type.

sqlite3_context is a opaque type when used out of vdbe.c and should not be dereferenced, since it's definition is incomplete at comptime.

https://github.com/tursodatabase/libsql/blob/be6a38fbd4d620b3d0f0d4c8962c9d5bdc339796/libsql-sqlite3/src/alter.c#L1868-L1870

This goes under the radar because of the "amalgamation" aproach to build the source. (Yet another drawback https://github.com/tursodatabase/libsql/issues/1028#issuecomment-2185625330). The solution is to #include "vdbeInt.h", but this is very smelly. If the type should be known by the whole source, better add it to sqlite3Int.h.

The func.c includes vdbeInt.h already.

https://github.com/tursodatabase/libsql/blob/af8239736b2d67c705728be45ba2f8ebe3ae6c1a/libsql-sqlite3/src/func.c#L23

Here is some docs:
https://github.com/tursodatabase/libsql/blob/be6a38fbd4d620b3d0f0d4c8962c9d5bdc339796/libsql-sqlite3/src/vdbeInt.h#L374-L398

Inspect the dereference in libsql-sqlite3/src/alter.c at lines 1868-1870, then compare the declarations in sqlite3Int.h and vdbeInt.h with the existing include in libsql-sqlite3/src/func.c. Check how a non-amalgamated build exposes sqlite3_context and determine which header should own its definition. Done means the source compiles without relying on amalgamation while preserving the intended opaque-type boundary.