feat: update maximum key/value length

[fmorency]

This PR updates the merk version used by the kvstore to allow value size larger than 64KiB.

The new limits are

• Key: 254 bytes (1 byte used for delimiter)
• Value: 512KiB

Fixes #346

Note: The merk version used in ledger is unchanged; only kvstore is affected by the update. Note2: merk still limits the key length to 255 bytes even if the underlying storage supports more. Not sure why but this is out of the scope of this PR.

[codecov[bot]]

Codecov Report

Merging #381 (f19a8cb) into main (1cb14b0) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #381   +/-   ##
=======================================
  Coverage   83.11%   83.12%           
=======================================
  Files         126      126           
  Lines       15335    15343    +8     
=======================================
+ Hits        12746    12754    +8     
  Misses       2589     2589           

Impacted Files	Coverage Δ
src/many-modules/src/_7_kvstore_commands/put.rs	95.31% <ø> (ø)
src/many-kvstore/src/module.rs	83.73% <100.00%> (+0.64%)	:arrow_up:
src/many-kvstore/src/module/account.rs	87.44% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[fmorency]

I thought the latest merk could also have bigger keys?

See the PR description :)