Address reviewer feedback:
- legacy regex was wrapping password: !secret name and clobbering
the dumper's user-friendly !secret round-trip; extend the negative
lookahead to skip !secret (and !lambda) values entirely
- drop the in-replacement !lambda check now that the lookahead handles it
- reword the thread-safety claim in dump() since _SECRET_VALUES /
_SECRET_CACHE remain module globals
- reword the SensitiveStr representer registration comment to reflect
PyYAML's MRO-walked dispatch rather than registration order
- tighten the legacy regex comment
Adds tests for the !secret and !lambda skip paths.
J. Nick Koston
bc2a811568