Drop parse_duration for fundu-systemd (#1246) (#1468)

`parse_duration` is no longer maintained upstream; `fundu-system` seems like the best option to provide most of the functionality provided by parse_duration and minimize deps.

Fixes #1246

Dep diffstat: +3 -6

## Caveats
- I've done basically no testing of this PR beyond `cargo test`
- See my comment in #1246 for regression risk; this is a breaking change. Is there a document I should update to make note of this? Should I rebase this for `next-v3` instead?
- In theory CVE-2021-29932 is fixed by this PR as `fundu-systemd` doesn't support exponents, but I've done no verification that this is really the case beyond the info in #1246

Reviewed-on: https://git.deuxfleurs.fr/Deuxfleurs/garage/pulls/1468
Reviewed-by: Alex <lx@deuxfleurs.fr>

src/model/Cargo.toml

@@ -30,7 +30,6 @@ thiserror.workspace = true
 hex.workspace = true
 http.workspace = true
 base64.workspace = true
-parse_duration.workspace = true
 tracing.workspace = true
 rand.workspace = true
 zstd.workspace = true

src/model/garage.rs

@@ -304,7 +304,7 @@ impl Garage {
 		self.k2v.spawn_workers(bg);
 
 		if let Some(itv) = self.config.metadata_auto_snapshot_interval.as_deref() {
-			let interval = parse_duration::parse(itv)
+			let interval = garage_util::time::parse_duration(itv)
 				.ok_or_message("Invalid `metadata_auto_snapshot_interval`")?;
 			if interval < std::time::Duration::from_secs(600) {
 				return Err(Error::Message(