Make test wasms build more consistently so they can be used in test snapshot tests

[leighmcculloch]

Make test wasms in this repo build more consistently.

So that disabling test snapshots does not have to be turned off in tests that use wasms:

rs-soroban-sdk/tests/alloc/src/test.rs

Lines 15 to 22 in 13263e8

	#[test]
	fn test() {
	let e = Env::new_with_config(EnvTestConfig {
	// Disable test snapshots because the tests in this repo will run across
	// multiple hosts, and this test uses a wasm file that won't build consistently
	// across different hosts.
	capture_snapshot_at_drop: false,
	});

The wasms in this repos CI are build using vanilla cargo build, which we know does not result in consistent builds.

Note that fixing this is relatively low priority, because most folks only need to build their wasm with one host. The wasms in this repo get built across a variety of hosts as part of multi-platform testing because the users of the SDK use a variety of hosts.

[leighmcculloch]

Possible ideas to try:

• Use cargo rustc with options like how stellar contract build does, that are designed to increase reproducibility.
• Wait for Only hash host-independent host-dependency metadata when cross-compiling rust-lang/cargo#15477
• Build the test wasms in a single host and then share them across the varied host builds (not great because we'd actually like to build and test them across hosts end-to-end)
• Commit the wasm files (not great because we want to build and test them across hosts end-to-end)
• Don't worry about it and keep using the disabled snapshot solution.

[leighmcculloch]

The problem is that the sdk version including the current commit sha gets built into the file, and the sdk version when built locally is prior to the commit where-as on CI is after the commit so the commit is different.