Don't copy contiguous bytes on reception (backport #343)

[mergify]

This uses the slices iterator API of zenoh-c to avoid unecessarily copying bytes into an owned slice, if and only if the bytes is made up of exactly one slice.

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This is an automatic backport of pull request #343 done by Mergify.

[mergify]

Cherry-pick of cebb972 has failed:

On branch mergify/bp/jazzy/pr-343
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Changes to be committed:
	modified:   rmw_zenoh_cpp/src/detail/rmw_subscription_data.cpp
	modified:   rmw_zenoh_cpp/src/detail/rmw_subscription_data.hpp

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   rmw_zenoh_cpp/src/detail/zenoh_utils.cpp
	both modified:   rmw_zenoh_cpp/src/detail/zenoh_utils.hpp

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