perf(ui/interfaces): halve per-interface HashMap lookups and drop a String clone on every render

[obchain]

Problem

In src/ui/tabs/interfaces.rs, inside the per-interface loop that runs every TUI frame, there are three small but avoidable costs:

1. Duplicate rates.get() call (lines 76 + 82)

let rx_rate_str = if let Some(rate) = rates.get(&stat.interface_name) {
    format!("{}/s", format_bytes(rate.rx_bytes_per_sec))
} else {
    "---".to_string()
};

let tx_rate_str = if let Some(rate) = rates.get(&stat.interface_name) {
    format!("{}/s", format_bytes(rate.tx_bytes_per_sec))
} else {
    "---".to_string()
};

rates is a HashMap<String, InterfaceRates>. Both lookups hash and compare the same key (stat.interface_name). A single let rate = rates.get(&stat.interface_name); binding covers both.

2. stat.interface_name.clone() (line 93)

Cell::from(stat.interface_name.clone())

stat is already borrowed (&InterfaceStats). Cell::from accepts &str via Into<Cell<'_>>, so the clone is unnecessary — stat.interface_name.as_str() suffices.

3. s.to_string() in the header closure (line 123)

let right = |s: &str| Cell::from(Line::from(s.to_string()).right_aligned());

All arguments are &'static str literals. Line::from(s) with s: &str is valid — the codebase already uses Line::from("...") throughout. The to_string() allocates a String only to construct a Line that could be built directly from the &str.

Fix

• Merge the two rates.get() calls into one binding.
• Replace stat.interface_name.clone() with stat.interface_name.as_str().
• Replace Line::from(s.to_string()) with Line::from(s) in the header closure.

All three are zero-behaviour-change refactors on the hot render path.

Impact

Per-frame, per-interface-entry: −1 HashMap hash+compare, −1 String clone. Per-frame in the header: −9 String allocations (one per column label).