(build) sets 1.95 as minimum supported and uses 1.95 for builds

[therapon]

• Cargo.toml sets minimum supported Rust version
• rust-toolchain.toml sets exact version to use for dev and ci

This PR sets both files to 1.95

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.85%. Comparing base (3731c8c) to head (8e0c97b).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1647   +/-   ##
=======================================
  Coverage   63.85%   63.85%           
=======================================
  Files          44       44           
  Lines        8121     8121           
=======================================
  Hits         5186     5186           
  Misses       2935     2935           

Flag	Coverage Δ
unittests	63.85% <ø> (ø)

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