"etc." is not recognized as the end of a sentence.

"etc." nor "etc.." seem to be recognized as the end of a sentence.

`long.md`:
```
This sentence is way too long for Harper, because it uses many words, but also
repeats itself, make overly long lists, insert nonsense, tell random stories
about life, etc. But it would help if it detected that it's actually two
sentences and not just one.
```

```
cargo run --bin harper-cli lint /tmp/long.md
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.08s
Running `target/debug/harper-cli lint /tmp/long.md`
/home/ux/.config/harper-ls/dictionary.txt: No such file or directory (os error 2)
/home/ux/.local/share/harper-ls/file_dictionaries/tmp%long.md%: No such file or directory (os error 2)
Advice:
╭─[long.md:1:1]
│
1 │ ╭─▶ This sentence is way too long for Harper, because it uses many words, but also
┆ ┆
4 │ ├─▶ sentences and not just one.
│ │
│ ╰───────────────────────────────── This sentence is 45 words long.
───╯
```

Tested with: Harper 0.37.0

Reproduce the report with the shown long.md content and run `cargo run --bin harper-cli lint /tmp/long.md`. Read the sentence-length diagnostic and the sentence-boundary handling it reaches. Done means the example is treated as two sentences when it contains `etc.` or `etc..`, rather than as one 45-word sentence.

Written by the indexing model from the issue text.