results: results.xy, a quantity against the load factor, time or mode (#94)

A nodal field at a node per frame (nonlinear static displacements from
load factor 0, explicit frames, heat temperatures) or per mode, the
explicit energies and histories, history nodes, and the frequencies or
buckling load factors; capped at 100000 points with `every`; stale
results refused; `path` writes a two-column CSV. XY Plot is ready.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/cmd/results.rs

@@ -112,7 +112,7 @@ fn solved_list(s: &Session) -> String {
 
 /// The steps a command works on.
 #[derive(Clone, Copy, PartialEq)]
-enum Want {
+pub(super) enum Want {
     Any,
     Frequency,
     /// Steps with frames: explicit dynamics and nonlinear static (one per converged increment).
@@ -138,7 +138,7 @@ impl Want {
 
 /// The step a command works on: `step`, else the step shown, else the first solved one
 /// (current results first) of the kind it wants.
-fn step_for(s: &Session, p: &Value, want: Want) -> Result<String> {
+pub(super) fn step_for(s: &Session, p: &Value, want: Want) -> Result<String> {
     if let Some(name) = opt::<String>(p, "step")? {
         if s.latest_result(&name).is_none() {
             return Err(EngineError::Params(format!("step `{name}` has no result; {}", solved_list(s))));
@@ -660,13 +660,13 @@ fn export_csv(s: &mut Session, p: &Value) -> Result<Value> {
 }
 
 /// A table of cells (a number, text, or empty) under a header, written as CSV.
-struct Table {
-    header: Vec<String>,
-    rows: Vec<Vec<Cell>>,
+pub(super) struct Table {
+    pub(super) header: Vec<String>,
+    pub(super) rows: Vec<Vec<Cell>>,
 }
 
 #[derive(Clone, Debug, PartialEq)]
-enum Cell {
+pub(super) enum Cell {
     Number(f64),
     Text(String),
     Empty,
@@ -675,7 +675,7 @@ enum Cell {
 impl Table {
     /// RFC 4180: comma-separated, CRLF line ends, a field with a comma, quote or line break in
     /// quotes (its quotes doubled); numbers in Rust's shortest round-trip form.
-    fn csv(&self) -> String {
+    pub(super) fn csv(&self) -> String {
         let field = |s: &str| if s.contains([',', '"', '\r', '\n']) { format!("\"{}\"", s.replace('"', "\"\"")) } else { s.to_string() };
         let mut out = String::new();
         let line = |cells: Vec<String>, out: &mut String| {