Replace grcov with tarpaulin for test coverage

[baszalmstra]

So from my point of view these are the pros and cons of using tarpaulin over grcov:

Pros

• Seems to give more precise coverage
• Better integration in the rust ecosystem
• Actively developed.

Cons

• Still has false positives
• Only runs on Ubuntu (so no coverage on macOS and Windows specific paths)
• Might still be unstable because it was in the past

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@00cb85a). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #100   +/-   ##
=========================================
  Coverage          ?   77.78%           
=========================================
  Files             ?      134           
  Lines             ?     8806           
  Branches          ?        0           
=========================================
  Hits              ?     6850           
  Misses            ?     1956           
  Partials          ?        0           

Impacted Files	Coverage Δ
crates/mun_hir/src/macros.rs	100.00% <0.00%> (ø)
crates/mun_codegen/src/intrinsics/macros.rs	100.00% <0.00%> (ø)
crates/mun_syntax/src/parsing/lexer/comments.rs	100.00% <0.00%> (ø)
crates/mun_hir/src/in_file.rs	45.45% <0.00%> (ø)
crates/mun_compiler/src/diagnostics/emit.rs	0.00% <0.00%> (ø)
crates/tools/src/runtime_capi.rs	100.00% <0.00%> (ø)
crates/mun_runtime/src/test.rs	97.99% <0.00%> (ø)
crates/mun_errors/src/location.rs	12.50% <0.00%> (ø)
crates/mun_syntax/src/tests/parser.rs	100.00% <0.00%> (ø)
crates/mun_hir/src/expr/validator/tests.rs	100.00% <0.00%> (ø)
... and 124 more

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