Build fixes and improvements

[rkistner]

This now adds explicit -Z build-std and --target specifiers to every release build.

The significant effects:

1. The --target ensures we actually build for the correct target. The current linux libpowersync_aarch64.so release is actually a x86_64 build.
2. build-std gives us a more optimized std-lib, and specifically removes any unwinding-related code. This reduces the output library size (241KB -> 173K for linux x86_64),
3. The above avoids undefined symbol: _Unwind_Resume or similar issues.

build-std also requires an explicit target.

Additionally, this fixes some linux targets incorrectly specified in .cargo/config.toml.

This specifically affects linux, macos and windows builds - will have to test each of those again. Android, iOS and WASM already used build-std, and are not affected.

This also fixes some issues in the release process:

• Only upload binaries in the release.yml workflow - the others were not used.
• Use gh release upload for binary uploads. The previous method created both a draft release and another published release; this now only creates a single draft.

Sizes of artifacts after these changes:

Note: Manually rebuilt libpowersync_aarch64.so for release 0.2.0, 0.2.1 and 0.3.0 to fix the build issue in current releases.

[mugikhan]

This makes the build process much simpler!