Refactor encoding version and flag to add more flags

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

Changes:

Currently, version number uses 1 byte and flags uses 1 byte.

We don't need 255 versions but we need more flags now in order to support atree inlining.

For now, reserve the first 4 bits for version (0-15), but also reserve the 5th bit separately so in the future, we can decide if we want to use 5th bit to have more versions (0-31) or a new flag.

So the first byte has (beginning with top bit): 1-4: version (0 to 15) and version 1 only uses 4th bit. 5: reserved to provide 16 more versions or another flag 6: reserved (use this for next new flag if needed) 7: slab has next slab ID (only relevant for data slab) 8: slab has inlined slabs (for atree inlining)

Atree inlining bumps version from 0 to 1. The top bit won't be needed until version 7, so it can be used to change this layout in the future if needed.

This PR is backward compatible and simpler than alternatives (e.g. doesn't reverse top bits, etc.).

[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 Report

Patch coverage: 62.23% and project coverage change: -0.40% :warning:

Comparison is base (74e19aa) 65.24% compared to head (a5c7323) 64.84%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #338 +/- ## ========================================== - Coverage 65.24% 64.84% -0.40% ========================================== Files 14 14 Lines 8761 8787 +26 ========================================== - Hits 5716 5698 -18 - Misses 2327 2356 +29 - Partials 718 733 +15 ``` | [Files Changed](https://app.codecov.io/gh/onflow/atree/pull/338?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=onflow) | Coverage Δ | | |---|---|---| | [basicarray.go](https://app.codecov.io/gh/onflow/atree/pull/338?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=onflow#diff-YmFzaWNhcnJheS5nbw==) | `49.36% <14.28%> (-0.42%)` | :arrow_down: | | [slab.go](https://app.codecov.io/gh/onflow/atree/pull/338?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=onflow#diff-c2xhYi5nbw==) | `66.66% <40.00%> (-33.34%)` | :arrow_down: | | [storable\_slab.go](https://app.codecov.io/gh/onflow/atree/pull/338?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=onflow#diff-c3RvcmFibGVfc2xhYi5nbw==) | `27.53% <50.00%> (-4.35%)` | :arrow_down: | | [encode.go](https://app.codecov.io/gh/onflow/atree/pull/338?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=onflow#diff-ZW5jb2RlLmdv) | `76.47% <57.14%> (-2.90%)` | :arrow_down: | | [array.go](https://app.codecov.io/gh/onflow/atree/pull/338?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=onflow#diff-YXJyYXkuZ28=) | `69.91% <60.25%> (-0.63%)` | :arrow_down: | | [map.go](https://app.codecov.io/gh/onflow/atree/pull/338?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=onflow#diff-bWFwLmdv) | `67.05% <64.10%> (-0.31%)` | :arrow_down: | | [flag.go](https://app.codecov.io/gh/onflow/atree/pull/338?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=onflow#diff-ZmxhZy5nbw==) | `74.21% <72.61%> (-2.06%)` | :arrow_down: |

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onflow / atree

Refactor encoding version and flag to add more flags #338

Codecov Report