HeatStressR 2.2.0

Added

• heat_indices() calculates multiple requested non-Liljegren indices from
  aligned observations, reusing shared validation and vapour-pressure work.
  wbgt.Bernard is available as an explicit opt-in when dew point is supplied.
• Reproducible benchmarks cover optimized non-Liljegren paths across cool,
  mixed, and hot inputs from 1 through 1,000,000 rows.

Changed

• wbgt.Bernard() uses a vectorized, bracketed bisection solver in place of
  one stats::optimize() call per valid row. Its public arguments and
  preprocessing behavior are unchanged.
• hi() evaluates the Rothfusz polynomial only for rows where it applies.
  It now returns degrees Celsius, matching its Celsius input and the rest of
  the package. To reproduce a previous Fahrenheit result, use
  hi(tas, hurs) * 1.8 + 32.
• Shared vapour-pressure work and small vector-allocation improvements reduce
  repeated computation in closed-form indices. Existing exported function
  names, formal arguments, positional calling conventions, and legacy
  unequal-length behavior of tashurs2vap.pres() and dewp2hurs() are
  retained.