test: generic extension unit testing

[chungquantin]

Test suite for modules in the generic extension crate:

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.92537% with 34 lines in your changes missing coverage. Please review.

Project coverage is 45.24%. Comparing base (7a20bb7) to head (456b0cd).

Files with missing lines	Patch %	Lines
extension/src/functions.rs	95.96%	0 Missing and 9 partials ⚠️
pallets/api/src/extension.rs	0.00%	6 Missing ⚠️
primitives/src/lib.rs	0.00%	6 Missing ⚠️
extension/src/lib.rs	96.34%	0 Missing and 3 partials ⚠️
extension/src/mock.rs	93.75%	2 Missing and 1 partial ⚠️
node/src/command.rs	0.00%	2 Missing ⚠️
runtime/devnet/src/config/xcm.rs	0.00%	2 Missing ⚠️
runtime/testnet/src/config/xcm.rs	0.00%	2 Missing ⚠️
extension/src/decoding.rs	99.32%	1 Missing ⚠️

@@                 Coverage Diff                 @@
##           frank/extension     #240      +/-   ##
===================================================
+ Coverage            35.84%   45.24%   +9.39%     
===================================================
  Files                   40       40              
  Lines                 3270     3698     +428     
  Branches              3270     3698     +428     
===================================================
+ Hits                  1172     1673     +501     
+ Misses                2039     1971      -68     
+ Partials                59       54       -5     

Files with missing lines	Coverage Δ
extension/src/matching.rs	100.00% <100.00%> (+54.54%)	⬆️
extension/src/tests.rs	97.22% <100.00%> (+5.81%)	⬆️
pallets/api/src/fungibles/mod.rs	82.96% <100.00%> (ø)
runtime/devnet/src/config/api/mod.rs	0.00% <ø> (ø)
runtime/devnet/src/config/api/versioning.rs	61.19% <100.00%> (+0.29%)	⬆️
runtime/devnet/src/config/proxy.rs	0.00% <ø> (ø)
runtime/devnet/src/lib.rs	17.31% <ø> (ø)
runtime/testnet/src/config/proxy.rs	0.00% <ø> (ø)
runtime/testnet/src/extensions.rs	0.00% <ø> (ø)
runtime/testnet/src/lib.rs	14.88% <ø> (ø)
... and 9 more

... and 1 file with indirect coverage changes

[evilrobot-01]

Just a partial review.

Looks great so far, left some comments.

[peterwht]

Amazing work!!! Really great coverage, the small test sizes made reviewing and understanding everything much easier.

Left some comments, but I can tell it's super close to being ready.