Use rustls and regex-lite; refactor HTTP API

Switch reqwest to rustls-no-provider and add rustls crate; install
rustls provider at startup. Replace regex::Regex with regex_lite::Regex
across code. Consolidate api_get/post/put/delete into a single
api_request that takes a Method and optional body. Add .dockerignore and
UPX compression in Dockerfile. Remove unused domain/IDNA code, trim dead
helpers, tweak tokio flavor and release opt-level, and update tests to
use crate::test_client()

Dockerfile

@@ -5,6 +5,7 @@ WORKDIR /build
 COPY Cargo.toml Cargo.lock ./
 COPY src ./src
 RUN cargo build --release
+RUN apk add --no-cache upx && upx --best --lzma target/release/cloudflare-ddns
 
 # ---- Release ----
 FROM scratch AS release