embassy-supervisor-syntax 0.3.1

Additive. embassy-supervisor-macros = "=0.9.1" and embassy-supervisor-tools
0.4.1 are the matching consumers.

Added

• dataflow_attr(&Attribute) -> Option<(Attribute, Option<String>)>: the
  dataflow attribute an attribute carries once cfg_attr is applied, plus
  the predicate it sits under (feature="grown"; nested layers fold into
  all(..)).

Fixed

• is_dataflow_attr and scan_dataflow now see a #[dataflow] written as
  #[cfg_attr(pred, dataflow)]. The compiler expands that form, so the
  tables were emitted while the textual scan skipped the fn. Accesses found
  this way carry pred in cfgs, as a #[cfg] on the fn would.
• Access::cfgs records a predicate once when the fn and the call site
  repeat it, instead of twice.