Reduce encoded size of map and bump version

[fxamacker]

Updates #292 Updates https://github.com/onflow/flow-go/issues/1744

Changes:

• bump Atree format version to 1 (was 0) for maps
• remove redundant version and flag data from root slabs (2 bytes per root slab)
• remove redundant slab address from children headers in metadata slab since all child slabs have the same address (8 bytes per child header per metadata slab)
• reduce encoded child slab size in children headers in metadata slab from 4 bytes to 2 bytes (2 bytes per child header per metadata slab)
• reduce encoded number of digests from 8 bytes to 2 bytes (6 bytes per data slab)
• reduce encoded number of map elements from 8 bytes to 2 bytes (6 bytes per data slab)
• decode version 0 and 1
• encode only version 1
• add tests to decode map slabs data in version 0

⚠️ This change requires data migration and data format version was bumped from 0 to 1.

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• [x] Targeted PR against main branch
• [x] Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• [x] Code follows the standards mentioned here
• [x] Updated relevant documentation
• [x] Re-reviewed Files changed in the Github PR explorer
• [x] Added appropriate labels

[codecov-commenter]

Codecov Report

Merging #331 (cb5d4b0) into main (06f4676) will increase coverage by 0.25%. Report is 4 commits behind head on main. The diff coverage is 68.95%.

@@            Coverage Diff             @@
##             main     #331      +/-   ##
==========================================
+ Coverage   65.04%   65.30%   +0.25%     
==========================================
  Files          14       14              
  Lines        8593     8761     +168     
==========================================
+ Hits         5589     5721     +132     
- Misses       2296     2323      +27     
- Partials      708      717       +9     

Files Changed	Coverage Δ
map.go	67.44% <68.84%> (+0.48%)	:arrow_up:
map_debug.go	52.45% <100.00%> (ø)

... and 1 file with indirect coverage changes