feat: raw data support (experimental)

[pi0]

Resolves #21
Resolves #121

This PR supports the storing and retrieval of raw values using the new getItemRaw/setItemRaw interface.

Drivers can opt-in to implement getItemRaw/setItemRaw as well. When they do, unstorage directly uses this interface instead of getItem/setItem.

For drivers not supporting raw format, unstorage uses a compatibility layer to serialize and deserialize raw values with base64: protocol. Raw input can be any value supported by [Buffer.from(https://nodejs.org/api/buffer.html). This support is now added for fs (node) and memory (universal)

Followup #142

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (main@ec7c7c2). Click here to learn what that means.
The diff coverage is 84.09%.

@@           Coverage Diff           @@
##             main     #141   +/-   ##
=======================================
  Coverage        ?   89.80%           
=======================================
  Files           ?       15           
  Lines           ?     1324           
  Branches        ?      299           
=======================================
  Hits            ?     1189           
  Misses          ?      135           
  Partials        ?        0           

Impacted Files	Coverage Δ
src/_utils.ts	85.71% <66.66%> (ø)
src/storage.ts	90.43% <85.71%> (ø)
src/drivers/fs.ts	94.33% <100.00%> (ø)
src/drivers/memory.ts	100.00% <100.00%> (ø)
src/drivers/utils/node-fs.ts	89.53% <100.00%> (ø)
src/types.ts	100.00% <100.00%> (ø)

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