Move providing responsabilities from bitswap to blockservice

[gammazero]

• bitswap/server: remove provide
• blockservice: add session workaround to work with wrapped blockservices
• blockservice: add WithProvider option
• blockservice: remove session embeding in context

Replaces #534 by @Jorropo which was outdated enough to make merging difficult.

[codecov]

Codecov Report

Attention: Patch coverage is 49.18033% with 31 lines in your changes missing coverage. Please review.

Project coverage is 60.17%. Comparing base (19a402b) to head (6af1b50).

Files with missing lines	Patch %	Lines
blockservice/blockservice.go	54.76%	13 Missing and 6 partials ⚠️
blockservice/providing_blockstore.go	14.28%	11 Missing and 1 partial ⚠️

@@            Coverage Diff             @@
##             main     #677      +/-   ##
==========================================
- Coverage   60.36%   60.17%   -0.20%     
==========================================
  Files         243      244       +1     
  Lines       30953    30867      -86     
==========================================
- Hits        18684    18573     -111     
- Misses      10612    10626      +14     
- Partials     1657     1668      +11     

Files with missing lines	Coverage Δ
bitswap/bitswap.go	69.51% <ø> (+2.07%)	⬆️
bitswap/options.go	33.33% <ø> (-3.04%)	⬇️
bitswap/server/server.go	55.73% <100.00%> (-8.19%)	⬇️
gateway/backend_blocks.go	45.64% <ø> (+0.15%)	⬆️
blockservice/providing_blockstore.go	14.28% <14.28%> (ø)
blockservice/blockservice.go	74.41% <54.76%> (-3.82%)	⬇️

... and 10 files with indirect coverage changes