Clear the clippy warnings, except the two that are not cosmetic

Down from 29 warnings to 2, in the spirit of 4ab95ff.

The doc warnings were all one mistake made repeatedly: a paragraph wrapped so
that a line *began* with `- ` or `+ `, which rustdoc reads as a markdown list
marker and the following lines as unindented continuations. The prose always
meant an em-dash. Fixed by moving the dash to the end of the previous line and
re-wrapping; not one word changed, which is the point - these comments record
things confirmed against real printers and are worth more than the warning.
The genuine lists just had their continuations de-indented and stayed lists.

The code ones are `match x { V(v) => .., _ => {} }` to `if let`, and nested
`if let Some(x) = .. { if cond { .. } }` to a let-chain. None had an `else`,
so each is the same control flow written once instead of twice.

Two warnings are left deliberately, because fixing them is not cosmetic:
`AmsTray` (544 bytes against 32) and `BambuReport` (984 against 120) both have
one variant far larger than the rest. The fix clippy wants is a `Box`, which
changes how every reader of those enums is written and puts an allocation on
the push_status path that currently has none. Worth measuring before doing,
not worth doing to silence a warning.

51 tests still pass.

src/printer/mod.rs

@@ -143,11 +143,12 @@ pub trait GenericPrinter {
 }
 
 /// M106's `S` parameter is a raw 0-255 PWM value, not a percentage. Shared
-/// by anything that ultimately sends gcode (Bambu, PrusaLink, PrusaSerial)
-/// - *not* a trait default, since Klipper's hypothetical native fan API
-/// below takes a percent directly and has no use for this at all. Private,
-/// but still visible to bambu.rs/prusa.rs: Rust's module privacy reaches
-/// into child modules, not just the exact file it's defined in.
+/// by anything that ultimately sends gcode (Bambu, PrusaLink,
+/// PrusaSerial) - *not* a trait default, since Klipper's hypothetical
+/// native fan API below takes a percent directly and has no use for this at
+/// all. Private, but still visible to bambu.rs/prusa.rs: Rust's module
+/// privacy reaches into child modules, not just the exact file it's defined
+/// in.
 fn percent_to_pwm(percent: u8) -> u8 {
     ((percent.min(100) as u16 * 255) / 100) as u8
 }