define and check minimum supported Rust version in CI

[tzemanovic]

Describe your changes

Our current MSRV is 1.80 because of orion dep that requires it

Checklist before merging

• If this PR has some consensus breaking changes, I added the corresponding breaking:: labels
  • This will require 2 reviewers to approve the changes
• If this PR requires changes to the docs or specs, a corresponding PR is opened in the namada-docs repo
  • Relevant PR if applies:
• If this PR affects services such as namada-indexer or namada-masp-indexer, a corresponding PR is opened in that repo
  • Relevant PR if applies:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.53%. Comparing base (b5f4a7d) to head (f037759).
Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4398   +/-   ##
=======================================
  Coverage   74.52%   74.53%           
=======================================
  Files         339      339           
  Lines      110504   110504           
=======================================
+ Hits        82351    82359    +8     
+ Misses      28153    28145    -8     

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[tzemanovic]

I'll move this into the new workflow added in #4401 once it's merge as we only need it for main PRs

[tzemanovic]

the new CI job can-backport fails because the cherry-pick resolves conflict in Cargo.toml badly (configured with --strategy-option=theirs it takes the libs version = "0.47.0" which must be on version = "0.47.3". Using ours strategy also doesn't work in this case as that omits the newly added rust-version field instead)