refactor: split the library into fumi-core and make it embeddable

Cargo.toml

@@ -1,34 +1,4 @@
-[package]
-name = "fumi"
-version = "0.1.0"
-edition = "2021"
-description = "Smol Mail client"
-license = "Apache-2.0"
-
-[[bin]]
-name = "fumi"
-path = "src/main.rs"
-
-[features]
-# RNS carrier over microReticulum (RNS.md); needs MICRORETICULUM_SOURCE_DIR
-# at build time, provided by the flake.
-rns = ["dep:cc"]
-
-[dependencies]
-snow = "0.9"
-chacha20poly1305 = "0.10"
-ed25519-dalek = { version = "2", features = ["rand_core"] }
-x25519-dalek = { version = "2", features = ["static_secrets"] }
-sha2 = "0.10"
-hmac = "0.12"
-hkdf = "0.12"
-rand_core = { version = "0.6", features = ["getrandom"] }
-rusqlite = { version = "0.32", features = ["bundled"] }
-data-encoding = "2"
-clap = { version = "4", features = ["derive"] }
-log = "0.4"
-env_logger = "0.11"
-anyhow = "1"
-
-[build-dependencies]
-cc = { version = "1", optional = true }
+[workspace]
+members = ["core", "cli"]
+default-members = ["cli"]
+resolver = "2"