Reduce the size of the future returned by async get_with and friend methods (v0.10)

[tatsuya6502]

This PR will mitigate #212 for upcoming Moka v0.10.0 release.

Changes

This PR does the same thing to PR #222, but on the master branch instead of the maint-09 branch.

future::Cache:

1. To mitigate current rustc's optimization issue, switched the internally using type for the init future from impl Future to a reference Pin<&mut impl Future>.
2. Eliminated an internal async function ValueInitializer:init_or_read(..., init, ...) from the call path.

Updated Methods:

future::Cache:

• get_with(...)
• get_with_if(...)
• optionally_get_with(...)
• try_get_with(...)
• get_with_by_ref(...)
• optionally_get_with_by_ref(...)
• try_get_with_by_ref(...)
• entry(...).or_insert_with(...)
• entry(...).or_insert_with_if(...)
• entry(...).or_optionally_insert_with(...)
• entry(...).or_try_insert_with(...)
• entry_by_ref(...).or_insert_with(...)
• entry_by_ref(...).or_insert_with_if(...)
• entry_by_ref(...).or_optionally_insert_with(...)
• entry_by_ref(...).or_try_insert_with(...)

[Swatinem]

Hm, The usage of macros is very interesting, I haven’t thought of that one. Though admittedly it is a bit sad that futures have such an overhead that one workaround is to replace them with something as unergonomic as macros. :-D

[tatsuya6502]

I will merge this into the master branch once all CI jobs are completed. I will do a squash merge.