Add update-sqlite-bundle.sh helper script

The steps to re-generate all the different variants of SQLite bundles is
a bit complicated. Add a script to automate that.

Author: penberg

scripts/update-sqlite-bundle.sh

@@ -0,0 +1,40 @@
+#!/bin/sh
+# Regenerate the bundled SQLite amalgamation and Rust bindings used by
+# libsql-ffi from the libsql-sqlite3 source tree.
+#
+# Outputs (relative to libsql-ffi/):
+#   bundled/src/sqlite3.c
+#   bundled/src/sqlite3.h
+#   bundled/bindings/bindgen.rs
+#   bundled/bindings/session_bindgen.rs
+#   bundled/SQLite3MultipleCiphers/src/sqlite3.c
+#   bundled/SQLite3MultipleCiphers/src/sqlite3.h
+#
+# The CI job in .github/workflows/c-bindings.yml validates the bundle by
+# running `cargo xtask build-bundled` and failing if it produces any diff.
+# That xtask only regenerates the C amalgamation (and copies it into both
+# bundled/src/ and bundled/SQLite3MultipleCiphers/src/); it does NOT
+# regenerate the bindgen files. So we do both here:
+#
+#   1. The LIBSQL_DEV builds regenerate the Rust bindings (bindgen.rs /
+#      session_bindgen.rs) via build.rs.
+#   2. `cargo xtask build-bundled` produces the canonical sqlite3.{c,h} in
+#      both bundled locations, byte-for-byte matching what CI checks.
+#
+# Run xtask last so the committed sqlite3.{c,h} are exactly the CI output.
+
+set -eux
+
+REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+
+# Step 1: regenerate the Rust bindings.
+cd "$REPO_ROOT/libsql-ffi"
+LIBSQL_DEV=1 cargo build
+LIBSQL_DEV=1 cargo build --features session
+LIBSQL_DEV=1 cargo build --features multiple-ciphers
+LIBSQL_DEV=1 cargo build --features session,multiple-ciphers
+
+# Step 2: regenerate the C amalgamation in both bundled locations using the
+# exact command CI validates against.
+cd "$REPO_ROOT"
+cargo xtask build-bundled