Internal optimisation

[zrzka]

Fixes #4

• Public API
  • There's no change, user still expects Result<Value>
  • Same applies to functions & filters, because signatures are part of the public API
• Private functions
  • Result<Cow<'a, Value>> is used instead of Result<Value>

There're probably more places suitable for optimisation, but I consider it as premature until benchmarks & friends will be implemented.

Change-type: patch Signed-off-by: Robert Vojta robert@balena.io