tidy-up: miscellaneous

- H3 proxy: re-sync code with original source `curl_ngtcp2.c` to reduce
  differences, and to apply missed minor fixes. Also apply clang-format.
  Drop redundant `#undef`s, casts, `#endif` comments, includes, drop
  intermediate variables, sync include and macro order.
  Follow-up to e78b1b3ecc #21153
- INSTALL-CMAKE.md: move `CURL_ENABLE_SMB` to the enable section.
- tests/http/env: rename `tcpdmp` to `tcpdump` to match object variable.
- mbedtls: drop incorrect `mbedTLS 4+` comments.
  (features are also supported by 3+, meaning it's always supported.)
- lib1648: rename a variable to match purpose.
- CIPHERS.md: alpha-sort link list.
- replace rare `X''` hex markup with `0x`.
- `IP v4/6` -> `IPv4/6`.
- 'version X.Y' -> 'vX.Y', where sensible.
- 'VX.Y' -> 'vX.Y', where sensible.
- fix indents, casing, newlines, typos.

Closes #21772

docs/RUSTLS.md

@@ -56,7 +56,7 @@ Once downloaded, build `curl` using `--with-rustls` and the path to the extracte
 Building `rustls-ffi` from source requires both a rust compiler, and the [cargo-c] cargo plugin.
 
 To install a Rust compiler, use [rustup] or your package manager to install
-the **1.73+** or newer toolchain.
+the **1.73** or newer toolchain.
 
 To install `cargo-c`, use your [package manager][cargo-c pkg], download
 [a pre-built archive][cargo-c prebuilt], or build it from source with `cargo install cargo-c`.