Chain Extension: Evaluation of method return type at compile time

[SkymanOne]

This PR closes #952

It introduces breaking changes to chain extension macro API: returns_result flag has been removed
Since this PR, Result<O, E> return type is detected and handled at the compile time.

If handle_status is set to true, the return type will still be wrapped into Result as before.

Tasks:

• Code cleanup
• Docs

[codecov-commenter]

Codecov Report

Merging #1569 (3edee36) into master (8321e6f) will increase coverage by 6.85%.
The diff coverage is 41.66%.

❗ Current head 3edee36 differs from pull request most recent head 1a40267. Consider uploading reports for the commit 1a40267 to get more accurate results

@@            Coverage Diff             @@
##           master    #1569      +/-   ##
==========================================
+ Coverage   64.68%   71.53%   +6.85%     
==========================================
  Files         207      205       -2     
  Lines        6417     6268     -149     
==========================================
+ Hits         4151     4484     +333     
+ Misses       2266     1784     -482     

Impacted Files	Coverage Δ
crates/env/src/chain_extension.rs	0.00% <0.00%> (ø)
crates/ink/ir/src/ir/attrs.rs	82.08% <ø> (+3.68%)	⬆️
crates/ink/macro/src/lib.rs	100.00% <ø> (ø)
crates/ink/tests/ui/chain_extension/E-01-simple.rs	3.12% <ø> (ø)
...rates/ink/codegen/src/generator/chain_extension.rs	95.23% <100.00%> (-0.51%)	⬇️
crates/ink/ir/src/ir/chain_extension.rs	93.33% <100.00%> (+22.74%)	⬆️
crates/env/src/call/create_builder.rs	0.00% <0.00%> (-2.64%)	⬇️
crates/allocator/src/bump.rs	88.23% <0.00%> (-0.85%)	⬇️
crates/e2e/src/xts.rs	0.00% <0.00%> (ø)
crates/e2e/src/client.rs	36.36% <0.00%> (ø)
... and 39 more

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[cmichi]

Not a fan of the > 80 CPL, but I see the surrounding code is using it too.