Limit usage of std::Instant to non-wasm targets

[TilBlechschmidt]

Effects

All uses of std::Instant are now limited to targets other than wasm32-*.
There should be no effect for targets other than WASM.

When targeting WebAssembly, it is now possible to use this library in environments where a time API is not available. For more details, see the original comment in #204

If this is a new feature or a bug fix ...

• Yes, the branch I'm proposing to merge is called issue-xyz where xyz is the number of the issue.

If this change adds or modifies a validation case

• No.
• Yes and:
  • I have coded up, or updated, an existing test case; and
  • I have provided a GMAT script which confirms the result(s); and
  • I have updated the VALIDATION.md file with the new error data between nyx and GMAT.
  • I will specify the version of GMAT used for the validation.

[TilBlechschmidt]

For most occurrences, I have simply gated the use. For a couple I decided to "duplicate" the message, removing the elapsed time.

In case of the rhapson- modules, an elapsed Duration is returned — those have been set to 0
_{(hope that's okay? No idea what they are used for down the line ...)}

---

The project compiles under both WASM and aarch64. It should be noted though that under WebAssembly the use of std::Instant does not fail to compile but instead throws a runtime exception.

[ChristopherRabotin]

Looks great, thanks!

Could you add a build step in the CI to build on wasm32? That'll just ensure that future changes don't break the build.

[TilBlechschmidt]

It appears that the check task already runs for the wasm32-unknown-unknown target:

nyx/.github/workflows/rust.yaml

Lines 32 to 33 in eec86a3

	- name: Run cargo check for WASM target
	run: cargo check --target wasm32-unknown-unknown

Corresponding action logs:
https://github.com/nyx-space/nyx/actions/runs/5674182922/job/15379332880?pr=205#step:5:1

It would probably be possible to make the test target work with wasm too but it appears as though it can't use tests with the regular #[test] macro. See wasm-bindgen-test for more details.

Note: Uses of std::Instant don't fail to compile, they throw runtime errors so check alone would not catch that.