Added Unit variant to execute and query fns

[Kayanski]

This PR aims at allowing projects to use unit variants in the ExecuteMsg and QueryMsg and still be able to use ExecuteFns and QueryFns.
An example usage is using cw-orch with Polytone : https://github.com/DA0-DA0/polytone/blob/a94feae54ee20cb51d8533d79229296e52164859/contracts/main/note/src/msg.rs#L59

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Latest commit:	2c15da3
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[codecov]

Codecov Report

Merging #196 (0cafc1c) into main (8c1d78e) will decrease coverage by 0.2%.
Report is 20 commits behind head on main.
The diff coverage is 87.9%.

❗ Current head 0cafc1c differs from pull request most recent head 2c15da3. Consider uploading reports for the commit 2c15da3 to get more accurate results

Files Changed	Coverage Δ
contracts/mock_contract_u64/src/lib.rs	48.9% <6.6%> (-19.6%)	⬇️
contracts/mock_contract/src/lib.rs	94.0% <92.8%> (-0.7%)	⬇️
packages/cw-orch-fns-derive/src/execute_fns.rs	99.1% <100.0%> (+2.6%)	⬆️
packages/cw-orch-fns-derive/src/query_fns.rs	100.0% <100.0%> (+2.3%)	⬆️

... and 9 files with indirect coverage changes

[Buckram123]

Nice improvement, few small nits

[Buckram123]

Nice, anything blocks it from opening pr?

[CyberHoward]

I'll leave merges on this repo to you @Kayanski from now on :)