Use grcov for code coverage

[thomcc]

actions-rs/tarpaulin has bitrotted. actions-rs/tarpaulin#21 (comment)

[codecov]

Codecov Report

Base: 65.64% // Head: 81.41% // Increases project coverage by +15.77% 🎉

Coverage data is based on head (2eb9363) compared to base (646c9c1).
Patch has no changes to coverable lines.

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #1274       +/-   ##
===========================================
+ Coverage   65.64%   81.41%   +15.77%     
===========================================
  Files          45       49        +4     
  Lines        3801     9878     +6077     
===========================================
+ Hits         2495     8042     +5547     
- Misses       1306     1836      +530     

Impacted Files	Coverage Δ
src/busy.rs	27.55% <0.00%> (-19.51%)	⬇️
src/params.rs	85.36% <0.00%> (-6.31%)	⬇️
src/util/param_cache.rs	95.00% <0.00%> (-5.00%)	⬇️
src/context.rs	37.20% <0.00%> (-3.97%)	⬇️
src/hooks.rs	80.54% <0.00%> (-3.79%)	⬇️
src/limits.rs	97.61% <0.00%> (-2.39%)	⬇️
src/version.rs	100.00% <0.00%> (ø)
libsqlite3-sys/src/lib.rs	100.00% <0.00%> (ø)
src/load_extension_guard.rs	0.00% <0.00%> (ø)
tests/vtab.rs	87.09% <0.00%> (ø)
... and 39 more

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