Set MSRV to 1.59 and update dependencies

[str4d]

Several dependencies remain un-upgraded:

• rpassword and clap are left as-is because our MSRV of 1.59 means using a cargo version that cannot handle the new weak or namespaced dependency features correctly (cargo <1.60 failed to select a version of a dependency due to either ? (weak) or dep: (namespaced) features rust-lang/cargo#10623).
• criterion is left as-is because the benchmarks use criterion-cycles-per-byte.

[codecov]

Codecov Report

Merging #349 (de96ae7) into main (a0ab691) will increase coverage by 0.11%.
The diff coverage is 31.81%.

@@            Coverage Diff             @@
##             main     #349      +/-   ##
==========================================
+ Coverage   38.66%   38.77%   +0.11%     
==========================================
  Files          34       34              
  Lines        3088     3092       +4     
==========================================
+ Hits         1194     1199       +5     
+ Misses       1894     1893       -1     

Impacted Files	Coverage Δ
age/src/encrypted.rs	43.47% <0.00%> (ø)
age/src/identity.rs	67.18% <0.00%> (ø)
age/src/ssh.rs	24.73% <ø> (ø)
age/src/primitives/armor.rs	41.33% <26.66%> (+0.09%)	⬆️
age-core/src/plugin.rs	31.09% <50.00%> (+0.37%)	⬆️
age/src/scrypt.rs	58.69% <100.00%> (ø)
age/src/primitives.rs	50.00% <0.00%> (-8.34%)	⬇️
age/src/protocol.rs	64.74% <0.00%> (-0.23%)	⬇️
age/src/format.rs	51.64% <0.00%> (ø)
... and 3 more

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