Update State::advance_time to be less indented (#1070)

### What does this PR do?

Following @goxberry's PR review on #1057 this PR attempts to remove the
heavy indentation in State::advance_time. Property tests from #1066 still
pass, so I'd say that was solid feedback. The code flows nicer now.

Author: blt

lading/proptest-regressions/generator/file_gen/logrotate_fs/model.txt

@@ -0,0 +1,8 @@
+# Seeds for failure cases proptest has generated in the past. It is
+# automatically read and these particular cases re-run before any
+# novel cases are generated.
+#
+# It is recommended to check this file in to source control so that
+# everyone who runs the test benefits from these saved cases.
+cc 14b817f8f064c889dabecae41294027ede294a5e51f613ddba46d8bb352f47f5 # shrinks to seed = 18077722532471589563, state = State { nodes: {2: Directory { name: "BUndwQB7", dir: Directory { children: {3}, parent: Some(1) } }, 1: Directory { name: "/", dir: Directory { children: {2}, parent: None } }, 3: File { file: File { parent: 2, bytes_written: 0, bytes_read: 0, access_tick: 0, modified_tick: 0, status_tick: 0, bytes_per_tick: 72, read_only: false, peer: None, ordinal: 0, group_id: 0, open_handles: 0, unlinked: false } }}, root_inode: 1, now: 0, max_rotations: 8, max_bytes_per_file: 32273, group_names: [["77sYYEM2_0.log", "77sYYEM2_0.log.1", "77sYYEM2_0.log.2", "77sYYEM2_0.log.3", "77sYYEM2_0.log.4", "77sYYEM2_0.log.5", "77sYYEM2_0.log.6", "77sYYEM2_0.log.7", "77sYYEM2_0.log.8"]], next_inode: 4, .. }, operations = [GetAttr, Read { offset: 873, size: 578 }, GetAttr, Wait { ticks: 67 }, Close, Open, Close, GetAttr, GetAttr, Open, GetAttr, Wait { ticks: 76 }, Wait { ticks: 90 }, Open, Wait { ticks: 73 }, Wait { ticks: 94 }, Close, Lookup { name: Some("¥'?*:𐠸𝜒A£⳾6?𐢬_Ѩ%ౝ0?{`.𑌂dM") }, Wait { ticks: 63 }, Open, Open, Open, Lookup { name: Some(";0$Ѩ¥𐖘Ⱥ.${*_:gn`Ⱥ\u{113d8}*Z") }, Open, Read { offset: 596, size: 401 }, Read { offset: 314, size: 229 }, Read { offset: 876, size: 934 }, Read { offset: 899, size: 782 }, Read { offset: 871, size: 732 }, Wait { ticks: 3 }, Read { offset: 986, size: 52 }, Lookup { name: None }, Lookup { name: None }, Read { offset: 586, size: 180 }, Close, Open, Lookup { name: Some("𞹾&Ⱥ<") }, GetAttr, Read { offset: 499, size: 626 }, Lookup { name: Some("𑥗%@�^ೋ𝄓") }, Read { offset: 625, size: 519 }, Open, Read { offset: 26, size: 857 }, GetAttr, Read { offset: 530, size: 378 }, Read { offset: 95, size: 717 }, GetAttr, Close, Read { offset: 119, size: 956 }, Open, GetAttr, Read { offset: 760, size: 956 }, Close, Wait { ticks: 98 }, Wait { ticks: 12 }, Read { offset: 138, size: 227 }, Wait { ticks: 41 }, GetAttr]
+cc 84a14bb361e5846589558e1fc52c5dee33d22e789034ef13c61f30ca4856d5da # shrinks to seed = 1512443422463708349, state = State { nodes: {1: Directory { name: "/", dir: Directory { children: {2}, parent: None } }, 2: Directory { name: "eKZTyj4p", dir: Directory { children: {3}, parent: Some(1) } }, 3: File { file: File { parent: 2, bytes_written: 0, bytes_read: 0, access_tick: 0, modified_tick: 0, status_tick: 0, bytes_per_tick: 4, read_only: false, peer: None, ordinal: 0, group_id: 0, open_handles: 0, unlinked: false } }}, root_inode: 1, now: 0, max_rotations: 2, max_bytes_per_file: 196227, group_names: [["F5Anm0dg_0.log", "F5Anm0dg_0.log.1", "F5Anm0dg_0.log.2"]], next_inode: 4, .. }, operations = [Wait { ticks: 40 }, Lookup { name: Some("𑌷C&𞺡\"?\"$<&%{$౿ோ") }, GetAttr, GetAttr, GetAttr, GetAttr, GetAttr, GetAttr, Wait { ticks: 17 }, Close, Read { offset: 225, size: 373 }, Wait { ticks: 34 }, Lookup { name: Some("ኻࠕN?¥<q*=%É\u{1d244}₹") }, Lookup { name: None }, Read { offset: 161, size: 111 }, Open, Lookup { name: None }, Wait { ticks: 24 }, Lookup { name: None }, Open, Lookup { name: Some("!*Ѩ𑼍ᛵﮩꬌῼ𞋿יּ:\"") }, Read { offset: 692, size: 769 }, Lookup { name: None }, Lookup { name: Some("𞅅.Ѩf$🉑{lⴧ\\\\?𞸻;સ./⋢ꚱÆᏽ`𐰃𖽻𐖇p𞋿h𝓂m{Z") }, Wait { ticks: 85 }, Open, Read { offset: 220, size: 438 }, Read { offset: 991, size: 393 }, Read { offset: 793, size: 379 }, Lookup { name: None }, GetAttr, Read { offset: 108, size: 606 }, Lookup { name: None }, Lookup { name: Some("𐖠\"n.[") }, Read { offset: 207, size: 867 }, Read { offset: 995, size: 862 }, GetAttr, Read { offset: 633, size: 542 }, Close, Close, Lookup { name: Some("Vպ۞.\"\"𐤈\\磌῞k`'𛲔\"�*|\\'{\u{b82}₻FᱤZP🕴.\\Ⱥ") }, GetAttr, GetAttr, Read { offset: 138, size: 921 }, Wait { ticks: 45 }]