`--budget` panics on an empty value, and treats NaN and infinity as no budget at all

[vyncint]

It panics

$ launchbound tune reduce-flip --backend model --cc 8.6 --budget ""
thread 'main' panicked at core/src/str/mod.rs:845:21:
end byte index 18446744073709551615 is out of bounds for string of length 0
$ echo $?
101

--budget " " does the same. crates/launchbound-cli/src/main.rs:

fn parse_budget(text: &str) -> anyhow::Result<f64> {
    let text = text.trim();
    let (digits, unit) = text.split_at(text.len() - 1);   // 0usize - 1

"".len() - 1 is usize::MAX. A trimmed-empty argument is the whole of it.

It accepts NaN and infinity, and they mean the opposite of a budget

$ launchbound tune ... --budget NaNs      # exit 0
$ launchbound tune ... --budget 1e400s    # exit 0

"NaN".parse::<f64>() succeeds; so does 1e400 (as inf). The value reaches
the guard in launchbound-bench/src/run.rs and launchbound-metal/src/lib.rs:

if let Some(budget) = options.budget_secs
    && sweep_started.elapsed().as_secs_f64() >= budget

x >= NaN is false for every x, and elapsed >= inf never becomes true.
So the branch never fires and the sweep runs to completion — unbounded.

That is not a cosmetic accept. --budget is how a measured run is bounded on
real silicon; a user who typed something that parsed to NaN gets an unbounded
--backend cuda sweep, believing it is capped. The one failure mode a budget
exists to prevent is the one it silently produces.

--budget 0 is the mirror image and is fine — the guard fires immediately and
the run reports budget exhausted after 0.0s: 0 of 11 candidates measured.

The errors are the float parser's, not the tool's

input	message
abc	error: invalid float literal
30min	error: invalid float literal
1hr	error: invalid float literal
s	error: cannot parse float from empty string

None names --budget, and none says what is accepted. 30min and 1hr are
what a person types; only 30m and 1h work, and nothing says so. Compare
--cc, which 2.0.0 taught to answer `abc` is not a compute capability — expected MAJOR.MINOR, e.g. `8.6`.

Fix

Parse it properly rather than by split_at(len - 1):

• an empty or whitespace argument is an error, not an index
• reject a value that is not finite and positive — is_finite() and > 0.0
  together close NaN, inf and negatives
• name the flag and the accepted forms in the message, and accept min/hr
  alongside m/h or say plainly that they are not accepted
• a unit-less number is currently taken as seconds; keep that, and say so

Worth a table test over "", " ", abc, 30min, 1hr, s, NaNs,
1e400s, 0, -5s, 30m, 90s, 1h, 45.

Done when

No input to --budget panics, nothing that parses to NaN or infinity is
accepted, and a rejected value is told what would have been accepted.