remove allocations from log machinery

[japaric]

see individual commits for details cc #746

[github-actions[bot]]

Number of dependencies and binary size impact report

Metric	main	PR #776	Delta
Direct dependencies	3	3	-
Total dependencies	4	4	-
Binary size	1022.2 KiB	1020.9 KiB	-0.1%
Text size	594.2 KiB	592.2 KiB	-0.3%

Dependencies diff

```diff └─ sudo-rs [v0.2.0] ├─ glob [v0.3.1] ├─ libc [v0.2.147] └─ log [v0.4.20] ```

[codecov[bot]]

Codecov Report

Patch coverage: 97.26% and project coverage change: +0.08% :tada:

Comparison is base (62aa93d) 55.24% compared to head (7bf365e) 55.33%. Report is 2 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #776 +/- ## ========================================== + Coverage 55.24% 55.33% +0.08% ========================================== Files 72 72 Lines 9841 9837 -4 ========================================== + Hits 5437 5443 +6 + Misses 4404 4394 -10 ``` | [Files Changed](https://app.codecov.io/gh/memorysafety/sudo-rs/pull/776?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=memorysafety) | Coverage Δ | | |---|---|---| | [src/log/syslog.rs](https://app.codecov.io/gh/memorysafety/sudo-rs/pull/776?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=memorysafety#diff-c3JjL2xvZy9zeXNsb2cucnM=) | `86.04% <96.15%> (+0.33%)` | :arrow_up: | | [src/log/simple\_logger.rs](https://app.codecov.io/gh/memorysafety/sudo-rs/pull/776?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=memorysafety#diff-c3JjL2xvZy9zaW1wbGVfbG9nZ2VyLnJz) | `100.00% <100.00%> (+13.63%)` | :arrow_up: | | [src/system/mod.rs](https://app.codecov.io/gh/memorysafety/sudo-rs/pull/776?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=memorysafety#diff-c3JjL3N5c3RlbS9tb2QucnM=) | `81.86% <100.00%> (-0.07%)` | :arrow_down: |

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