Remove host_print_writer from the arguments to UninitializedSandbox::new

[jprendes]

With #480 merged, registering a host function with a name that is already in use, just replaces the previous registration.
This means that we can pre-emptively register the default HostPrint method, and replace it afterwards.

This PR removes host_print_writer from the arguments to UninitializedSandbox::new.
The default host print is pre-emptively registered, and a new HostPrint can be registered like any other host function.
Alternatively, the method register_print can be used, which uses the correct name and (compile-time-)checks the function signature.

This partly addresses the following comment (i.e., it still doesn't implement a builder pattern, but does allow adding extra syscalls to the writer method)

hyperlight/src/hyperlight_host/src/sandbox/uninitialized.rs

Lines 195 to 197 in a862d4a

	// TODO: These only here to accommodate some writer functions.
	// We should modify the `UninitializedSandbox` to follow the builder pattern we use in
	// hyperlight-wasm to allow the user to specify what syscalls they need specifically.

[jprendes]

@danbugs @ludfjig PTAL :-)

[ludfjig]

LGTM. Could you update the example in the root README as well?

Fixed

[danbugs]

LGTM

Other than the README, you might want to check doctests! IIrc, we have 1 that might create an uninit sandbox.

[jprendes]

@danbugs @ludfjig PTAL :-)
Basically rebased and fixed doctest.