documents for new features and fixes added

docs/build-cleanup-chrono.md

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+Technical Task: Build Fixes & Profiler Cleanup
+Date: 2025-11-21 Goal: Fix PyPI build failures and remove heavy profiling code from production wheels.
+
+1. Fix PyPI Build Failure (chrono-tz)
+   Issue: The build fails on Linux/Mac/Windows CI because chrono-tz requires complex C-bindings that are often missing in standard Python environments. Analysis: UncheckedIO returns Apache Arrow RecordBatch objects (where timestamps are raw i64). We do not need pyo3 to convert Rust chrono types directly to Python datetime objects. The chrono-tz feature in pyo3 is dead weight causing build failures.
+
+Action: Update Cargo.toml to remove the conflicting feature.
+
+Ini, TOML
+
+# Cargo.toml
+
+# OLD
+# pyo3 = { version = "0.27.1", features = ["extension-module", "chrono-tz"] }
+
+# NEW (Remove "chrono-tz")
+pyo3 = { version = "0.27.1", features = ["extension-module"] }
+2. Productionize the Profiler (Remove Tracy)
+   Issue: The tracy-client and tracing-tracy crates add significant binary size and runtime overhead. They should not be present in the production library installed by users. Solution: Use Rust Feature Flags to make profiling "opt-in" for development only.
+
+Step A: Update Cargo.toml Define a profiling feature and make the heavy dependencies optional.
+
+Ini, TOML
+
+[features]
+default = []
+# The "profiling" feature enables these two optional crates
+profiling = ["dep:tracing-tracy", "dep:tracy-client"]
+
+[dependencies]
+# Keep this (Lightweight facade)
+tracing = "0.1.41"
+
+# Make these OPTIONAL (Heavy implementation)
+tracing-tracy = { version = "0.11.2", optional = true }
+tracy-client = { version = "0.17.6", optional = true }
+
+# ... other dependencies ...
+Step B: Update src/lib.rs Wrap the profiler initialization logic so it only compiles when the flag is active.
+
+Rust
+
+// src/lib.rs
+
+#[pymodule]
+fn unchecked_io(_py: Python<'_>, m: &Bound<'_, PyModule>) -> PyResult<()> {
+
+    // --- START PROFILER LOGIC ---
+    // This block now ONLY compiles if you run with `--features profiling`
+    #[cfg(feature = "profiling")] 
+    {
+        use tracing_subscriber::layer::SubscriberExt;
+        use tracing_subscriber::util::SubscriberInitExt;
+        
+        // Initialize the Tracy layer
+        let _ = tracing_subscriber::registry()
+            .with(tracing_tracy::TracyLayer::default())
+            .try_init();
+            
+        println!("--- UncheckedIO: Profiling Enabled (Tracy) ---");
+    }
+    // --- END PROFILER LOGIC ---
+
+    m.add_function(wrap_pyfunction!(load_data_from_config, m)?)?;
+    m.add_function(wrap_pyfunction!(to_pandas_dataframe, m)?)?;
+    m.add_function(wrap_pyfunction!(profile_data, m)?)?;
+    Ok(())
+}
+3. How to Build
+   For Development (With Profiler): Use this when you want to see the tracks in the Tracy GUI.
+
+Bash
+
+maturin develop --features profiling
+For Production / PyPI (Zero Overhead): This builds the "clean" version for users. The profiler code is stripped out entirely.
+
+Bash
+
+maturin publish