rpc: Add `FromStr`, `Serialize` and `Deserialize` instances to `CompatMode`

[romac]

Closes: #1374

• [x] Referenced an issue explaining the need for the change
• [x] Updated all relevant documentation in docs
• [x] Updated all code comments where relevant
• [x] Wrote tests
• [x] Added entry in .changelog/

[codecov-commenter]

Codecov Report

Merging #1367 (2b9c024) into main (bcc0b37) will increase coverage by 0.0%. The diff coverage is 71.7%.

:exclamation: Current head 2b9c024 differs from pull request most recent head eb7ff64. Consider uploading reports for the commit eb7ff64 to get more accurate results

@@          Coverage Diff          @@
##            main   #1367   +/-   ##
=====================================
  Coverage   61.2%   61.2%           
=====================================
  Files        274     274           
  Lines      26844   26890   +46     
=====================================
+ Hits       16433   16466   +33     
- Misses     10411   10424   +13     

Files	Coverage Δ
rpc/src/error.rs	95.6% <100.0%> (+0.2%)	:arrow_up:
rpc/src/client/compat.rs	79.3% <63.8%> (-10.9%)	:arrow_down:

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[romac]

Looks like the test coverage job is failing because of changes in supported unstable flags on nightly:

error: failed to run `rustc` to learn about target-specific information
error: unknown unstable option: `instrument-coverage`