added code coverage script and badges

scripts/coverage.sh

@@ -0,0 +1,62 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+repo_root="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+cd "$repo_root"
+
+if ! command -v rustup >/dev/null 2>&1; then
+  echo "rustup is required to manage Rust toolchain components." >&2
+  exit 1
+fi
+
+if ! command -v cargo >/dev/null 2>&1; then
+  echo "cargo is required to run coverage." >&2
+  exit 1
+fi
+
+if ! rustup component list --installed | grep -Eq '^llvm-tools(-preview)?($|-)'; then
+  echo "Missing rustup component: llvm-tools (aka llvm-tools-preview)." >&2
+  echo "Install with: rustup component add llvm-tools-preview" >&2
+  exit 1
+fi
+
+if ! cargo llvm-cov --version >/dev/null 2>&1; then
+  echo "Missing cargo subcommand: cargo-llvm-cov" >&2
+  echo "Install with: cargo install --locked cargo-llvm-cov" >&2
+  exit 1
+fi
+
+coverage_dir="target/llvm-cov"
+lcov_path="${coverage_dir}/lcov.info"
+html_dir="${coverage_dir}/html"
+
+mkdir -p "$coverage_dir"
+
+cargo llvm-cov \
+  --workspace \
+  --exclude gitcomet-ui \
+  --exclude gitcomet-ui-gpui \
+  --no-default-features \
+  --features gix \
+  --lcov \
+  --output-path "$lcov_path" \
+  "$@"
+
+cargo llvm-cov \
+  --workspace \
+  --exclude gitcomet-ui \
+  --exclude gitcomet-ui-gpui \
+  --no-default-features \
+  --features gix \
+  --html \
+  --output-dir "$html_dir" \
+  --no-run \
+  "$@"
+
+if [[ -f "$lcov_path" && -f "${html_dir}/index.html" ]]; then
+  echo "Coverage summary generated."
+  echo "LCOV report: ${repo_root}/${lcov_path}"
+  echo "HTML report: ${repo_root}/${html_dir}/index.html"
+else
+  echo "cargo llvm-cov completed."
+fi