[MayCXC]

Compiled with -DSQLITE_CORE, as when sqlite-vec.c is built into SQLite or into an application, sqlite3_vec_init() never reads its pApi parameter: SQLITE_EXTENSION_INIT2() is its only use, and SQLITE_CORE leaves it out. A project that compiles the file into its own binary with -Wall -Wextra gets a warning for it from main, with gcc 14.2 and with clang 19.1:

$ ./scripts/vendor.sh && make sqlite-vec.h
$ gcc -Ivendor -Wall -Wextra -DSQLITE_CORE -DSQLITE_VEC_STATIC -c sqlite-vec.c -o vec.o
...
sqlite-vec.c:10633:65: warning: unused parameter 'pApi' [-Wunused-parameter]
...

The Makefile's static target compiles without -Wall -Wextra, so the project's own builds do not print it. The same command prints 12 other warnings with gcc (sign comparisons, variables it reports as maybe used uninitialized, and an unused p_vector parameter in sqlite-vec-diskann.c), and the p_vector one with clang; this PR leaves those as they are.

sqlite3_vec_init() now marks pApi with UNUSED_PARAMETER() in the SQLITE_CORE case. The change comes from photostructure#9 (d89dbcf), and is open on vlasky/sqlite-vec as vlasky#23, where sqlite3_vec_numpy_init() and sqlite3_vec_static_blobs_init() have the same warning. No other open or closed PR or issue here marks it.

Test. The command above prints the pApi warning on main and not on this branch, with either compiler. UNUSED_PARAMETER() is a (void) cast, so the object files are byte-identical before and after, both for the loadable extension and with -DSQLITE_CORE. The Python tests (tests/test-*.py: 239 passed, 66 skipped) pass. make test-unit does not compile on main; with #305 and #319 merged it compiles and passes on Linux arm64, with this change and without it. (#305 alone fails there, in test_vec0_parse_partition_key_definition's empty-definition case: the && guards #319 corrects read the scanner's token after it found none, so the result depends on what the stack held.) It merges cleanly with #327 to #331 and #336 to #340.