transaction/fee: don't use fmt with "{.1}" to reduce binary size

Using this pulls in
`core::fmt::float::float_to_decimal_common_shortest` into the binary,
which is a huge function.

By changing the impl to something simpler, we save 20112 bytes in the
binary :O

We also add a CI check to avoid re-introducing this function in the
future by accident.

Author: benma

.ci/ci

@@ -53,6 +53,13 @@ make -j8 factory-setup
 make -j8 bootloader-semihosting
 make -j8 firmware-semihosting
 
+# Disallow some symbols in the final binary that we don't want.
+if arm-none-eabi-nm build/bin/firmware.elf | grep -q "float_to_decimal_common_shortest"; then
+    echo "Rust fmt float formatting like {.1} adds significant binary bloat."
+    echo "Use something simpler like (float*10).round() as u64, then format with util::decimal::format"
+    exit 1
+fi
+
 (cd tools/atecc608; go test ./...)
 
 # Don't generate graphics in CI

src/rust/bitbox02-rust/Cargo.toml

@@ -38,7 +38,7 @@ sha3 = { workspace = true, optional = true }
 digest = "0.10.6"
 zeroize = { workspace = true }
 num-bigint = { workspace = true, optional = true }
-num-traits = { version = "0.2", default-features = false, optional = true }
+num-traits = { version = "0.2", default-features = false }
 # If you change this, also change src/rust/.cargo/config.toml.
 bip32-ed25519 = { git = "https://github.com/digitalbitbox/rust-bip32-ed25519", tag = "v0.1.2", optional = true }
 bech32 = { version = "0.11.0", default-features = false, features = ["alloc"], optional = true }
@@ -74,7 +74,6 @@ app-ethereum = [
   "erc20_params",
   "sha3",
   "num-bigint",
-  "num-traits",
   # enable this feature in the deps
   "bitbox02/app-ethereum",
 ]

src/rust/bitbox02-rust/src/workflow/transaction.rs

@@ -35,7 +35,8 @@ pub async fn verify_recipient(recipient: &str, amount: &str) -> Result<(), UserA
 }
 
 fn format_percentage(p: f64) -> String {
-    format!("{:.1}", p)
+    let int: u64 = num_traits::float::FloatCore::round(p * 10.) as _;
+    util::decimal::format_no_trim(int, 1)
 }
 
 pub async fn verify_total_fee(