Add piecewise linear codec, deprecate linear and mulitinear, complete benchmark with real world datasets.

[fmassot]

Ok PR is ready for review.

Here is a summary of the PR:

• Piecewise linear codec added: basically it's a refactor and it fixes #1215
• #1212 partially fixed that by saving 8 bytes.
• Linear interpolation and multilinear deprecated. It's now only there for the reading part so that users can still read these fast field codecs
• FOR codec added with feature unstable, it's not used in tantivy for the moment.
• Bench also compression time/reading time and on real-world datasets.

[codecov-commenter]

Codecov Report

Merging #1217 (53785d5) into main (c503c6e) will decrease coverage by 0.20%. The diff coverage is 82.59%.

@@            Coverage Diff             @@
##             main    #1217      +/-   ##
==========================================
- Coverage   94.04%   93.84%   -0.21%     
==========================================
  Files         205      207       +2     
  Lines       34525    35023     +498     
==========================================
+ Hits        32470    32868     +398     
- Misses       2055     2155     +100     

Impacted Files	Coverage Δ
fastfield_codecs/src/main.rs	0.54% <0.00%> (-0.40%)	:arrow_down:
fastfield_codecs/src/linearinterpol.rs	95.15% <92.85%> (-4.39%)	:arrow_down:
fastfield_codecs/src/frame_of_reference.rs	94.70% <94.70%> (ø)
src/fastfield/serializer/mod.rs	92.94% <95.00%> (+2.94%)	:arrow_up:
fastfield_codecs/src/piecewise_linear.rs	97.64% <97.64%> (ø)
fastfield_codecs/src/bitpacked.rs	100.00% <100.00%> (ø)
fastfield_codecs/src/lib.rs	96.92% <100.00%> (+0.04%)	:arrow_up:
fastfield_codecs/src/multilinearinterpol.rs	97.11% <100.00%> (-0.93%)	:arrow_down:
src/fastfield/mod.rs	92.30% <100.00%> (-0.02%)	:arrow_down:
src/fastfield/reader.rs	81.74% <100.00%> (-13.17%)	:arrow_down:
... and 35 more

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[fmassot]

@PSeitz @fulmicoton : here is my take on what to do for next tantivy release and what to do after:

These remarks are valid for integers only (for floats, our codecs are useless):

• piecewise linear interpolation should have the best compression ratio for monotonically increasing series
• bitpacking should have the best compression ratio on random stuff
• frame of reference (FOR) should have the best compression for series in between

What can we do for tantivy next release?

• unplug linear interpolation and replace multilinear interpolation by new piecewise linear interpolation (the bug fix increases a little bit the compression ratio but nothing noteworthy)
• update the benchmark with new datasets
• I don't want to plug immediately the FOR stuff because I think we can do slightly better and I would also want to activate piecewise interpolation only on monotonically increasing series, I would introduce that later.

Future work:

• finalize the FOR codecs, activate piecewise linear for only monotonically increasing series
• sparse codecs
• float codecs

[fulmicoton]

@fmassot agreeing with the above.

[codecov-commenter]

Codecov Report

Merging #1217 (14d5385) into main (447811c) will decrease coverage by 0.26%. The diff coverage is 82.67%.

@@            Coverage Diff             @@
##             main    #1217      +/-   ##
==========================================
- Coverage   94.23%   93.97%   -0.27%     
==========================================
  Files         232      234       +2     
  Lines       40850    41414     +564     
==========================================
+ Hits        38496    38919     +423     
- Misses       2354     2495     +141     

Impacted Files	Coverage Δ
fastfield_codecs/src/main.rs	0.54% <0.00%> (-0.40%)	:arrow_down:
fastfield_codecs/src/linearinterpol.rs	95.15% <92.85%> (-4.39%)	:arrow_down:
fastfield_codecs/src/frame_of_reference.rs	94.73% <94.73%> (ø)
src/fastfield/serializer/mod.rs	92.85% <95.23%> (+1.55%)	:arrow_up:
fastfield_codecs/src/piecewise_linear.rs	97.63% <97.63%> (ø)
fastfield_codecs/src/bitpacked.rs	100.00% <100.00%> (ø)
fastfield_codecs/src/lib.rs	96.92% <100.00%> (+0.04%)	:arrow_up:
fastfield_codecs/src/multilinearinterpol.rs	97.08% <100.00%> (-1.93%)	:arrow_down:
src/fastfield/mod.rs	92.93% <100.00%> (-0.02%)	:arrow_down:
src/fastfield/reader.rs	76.37% <100.00%> (-12.70%)	:arrow_down:
... and 11 more

---

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