Build with NDK 28 or newer for 16KB page alignment

[simolus3]

Starting this November, virtually all Android apps are required to support running with 16KB page sizes enabled.

At the moment, the library we build for Android is 4KB-aligned.

$ ~/Library/Android/sdk/ndk/28.1.13356709/toolchains/llvm/prebuilt/darwin-x86_64/bin/llvm-objdump -p libpowersync.so | grep LOAD
    LOAD off    0x0000000000000000 vaddr 0x0000000000000000 paddr 0x0000000000000000 align 2**12
    LOAD off    0x000000000001c78c vaddr 0x000000000001d78c paddr 0x000000000001d78c align 2**12
    LOAD off    0x0000000000050c00 vaddr 0x0000000000052c00 paddr 0x0000000000052c00 align 2**12
    LOAD off    0x0000000000052698 vaddr 0x0000000000055698 paddr 0x0000000000055698 align 2**12

When using cargo-ndk with NDK 28 or above, it generates 16KB-aligned libraries by default:

$ ~/Library/Android/sdk/ndk/28.1.13356709/toolchains/llvm/prebuilt/darwin-x86_64/bin/llvm-objdump -p build/intermediates/jniLibs/arm64-v8a/libpowersync.so | grep LOAD
    LOAD off    0x0000000000000000 vaddr 0x0000000000000000 paddr 0x0000000000000000 align 2**14
    LOAD off    0x000000000001d004 vaddr 0x0000000000021004 paddr 0x0000000000021004 align 2**14
    LOAD off    0x0000000000050f10 vaddr 0x0000000000058f10 paddr 0x0000000000058f10 align 2**14
    LOAD off    0x00000000000529e8 vaddr 0x000000000005e9e8 paddr 0x000000000005e9e8 align 2**14

This can also be achieved with a linker option we could set in cargo, but updating the NDK and then relying on the default options sounds easier.

I've validated these changes by running a Flutter demo app on a 16KB emulator.