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`parse_duration` is no longer maintained upstream; `fundu-system` seems like the best option to provide most of the functionality provided by parse_duration and minimize deps.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

Cargo.toml

@@ -53,6 +53,8 @@ cfg-if = "1.0"
 chrono = { version = "0.4", features = ["serde"] }
 crc-fast = "1.9"
 crypto-common = "0.1"
+fundu = "2.0"
+fundu-systemd = "0.3"
 gethostname = "1.1"
 git-version = "0.3"
 hex = "0.4"
@@ -68,7 +70,6 @@ mktemp = "0.5"
 nix = { version = "0.31", default-features = false, features = ["fs"] }
 nom = "8.0"
 parking_lot = "0.12"
-parse_duration = "2.1"
 paste = "1.0"
 pin-project = "1.1"
 pnet_datalink = "0.35"