this commit alters the signature of the `EncodeLabelSet::encode()` trait
method, such that it now accepts a mutable reference to its encoder.

this is related to #135, and is a second proposal following
previous work in #240.

this change permits distinct label sets to be composed together, now
that the label set encoder is not consumed. a new implementation for
tuples `(A, B)` is provided.

this commit includes a test case showing that a metric family can
compose two label sets together, and that such a family can successfully
be digested by the python client library.

`derive-encode` is altered to generate code matching this new trait
signature, and has been bumped to version 0.5.0 as a result of this
breaking change in the `prometheus-client` library.

Signed-off-by: katelyn martin <me+cratelyn@katelyn.world>

fixes #231.

this introduces a new method to `Family<S, M, C>` to help alleviate the
risk of deadlocks when accessing multiple series within a given metrics
family.

this returns a plain `M`, rather than the `MappedRwLockReadGuard<M>`
RAII guard returned by `get_or_create()`.

a test case is introduced in this commit to demonstrate that structures
accessing multiple series within a single expression will not
accidentally create a deadlock.

Signed-off-by: katelyn martin <me+cratelyn@katelyn.world>

Signed-off-by: Edwin Amsler <edwinguy@gmail.com>

Signed-off-by: Max Leonard Inden <mail@max-inden.de>

According to [1]:
> Generally all macros (procedural as well as macro_rules) designed to be used
> by other people should refer to every single thing in their expanded code
> through an absolute path, such as std::result::Result.

[1]: https://github.com/dtolnay/proc-macro-workshop/blob/3b6bcd2c3ad1c1946e6fbcc9be25d3890876087d/builder/tests/09-redefined-prelude-types.rs#L13C1-L15C58

Signed-off-by: ADD-SP <add_sp@outlook.com>

Signed-off-by: Max Leonard Inden <mail@max-inden.de>

Signed-off-by: slonkazoid <slonkazoid@slonk.ing>

Signed-off-by: Ivan Babrou <github@ivan.computer>

Signed-off-by: hanabi1224 <harlowmoo@gmail.com>

Signed-off-by: Ivan Babrou <github@ivan.computer>

Signed-off-by: Max Leonard Inden <mail@max-inden.de>