Validate a TOTP code before saving it (#1055)

In order to do this, I had to remove the very old and unmaintainted
`otplib` and replace it with the well-maintained
[otpauth](https://www.npmjs.com/package/otpauth).

I kept the parameters the same, but if there is something only slightly
off between the two libraries, this could cause a major headache. I am
unsure on how to test this though, or if we can provide some sort of
migration for this.

The reason for the upgrade is two-fold:

1. As I said, the original library was unmaintained
2. It's verification mechanism relied on a Buffer class that, as far as
I can tell, can't work without some `require` statements that are
missing from the library's source files.

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Eugene <inbox@null.page>

.cargo/config.toml

@@ -1,2 +1,6 @@
-[build]
-rustflags = ["--cfg", "tokio_unstable"]
+#[build]
+#rustflags = ["--cfg", "tokio_unstable"]
+
+# https://github.com/rust-lang/cargo/issues/5376#issuecomment-2163350032
+[target.'cfg(all())']
+rustflags = ["--cfg", "tokio_unstable"]

.gitignore

@@ -22,3 +22,7 @@ config.yaml
 __pycache__
 .pytest_cache
 dhat-heap.json
+
+# IntelliJ based IDEs
+.idea/
+/.data/