[ci] #2153: Fix coverage

[s8sato]

Description of the Change

1. Resolve the toolchain differences around llvm-tools-preview

2. Move the coverage tool from grcov to cargo-llvm-cov ?

Issue

• Closes Fix coverage #2153

Benefits

1. Fix the CI failure

Possible Drawbacks

2. Not sure how long cargo-llvm-cov will be maintained

[codecov]

Codecov Report

Merging #2154 (cf48df6) into iroha2-dev (a8e011a) will increase coverage by 78.84%.
The diff coverage is n/a.

❗ Current head cf48df6 differs from pull request most recent head 502289e. Consider uploading reports for the commit 502289e to get more accurate results

@@               Coverage Diff               @@
##           iroha2-dev    #2154       +/-   ##
===============================================
+ Coverage            0   78.84%   +78.84%     
===============================================
  Files               0      125      +125     
  Lines               0    22308    +22308     
===============================================
+ Hits                0    17588    +17588     
- Misses              0     4720     +4720     

Impacted Files	Coverage Δ
telemetry/src/futures.rs	25.45% <0.00%> (ø)
data_model/src/pagination.rs	77.94% <0.00%> (ø)
data_model/src/events/mod.rs	49.09% <0.00%> (ø)
data_model/src/isi.rs	87.98% <0.00%> (ø)
...ions_validators/src/private_blockchain/register.rs	40.90% <0.00%> (ø)
client/src/config.rs	69.35% <0.00%> (ø)
data_model/src/events/data/events.rs	38.80% <0.00%> (ø)
core/src/smartcontracts/isi/tx.rs	40.00% <0.00%> (ø)
cli/src/torii/routing.rs	82.29% <0.00%> (ø)
telemetry/src/config.rs	64.70% <0.00%> (ø)
... and 115 more

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