refactor: Remove lifetime from Context, ResponseFuture, InterceptorFuture

[Xuanwo]

This PR will fix #403

The benchmark seems can't reflect the actual improvement. (I guess the test case(64K) is not suitable to measure the different between an Arc::new)

Before:

download 64K: isahc     time:   [201.80 ms 204.40 ms 207.00 ms]

After

download 64K: isahc     time:   [200.32 ms 203.57 ms 206.90 ms]

[codecov]

Codecov Report

Merging #405 (683bd9e) into master (352fbbc) will increase coverage by 0.14%.
The diff coverage is 92.30%.

@@            Coverage Diff             @@
##           master     #405      +/-   ##
==========================================
+ Coverage   51.94%   52.09%   +0.14%     
==========================================
  Files          52       52              
  Lines        5796     5787       -9     
==========================================
+ Hits         3011     3015       +4     
+ Misses       2785     2772      -13     

Impacted Files	Coverage Δ
src/interceptor/mod.rs	0.00% <0.00%> (ø)
src/request.rs	53.94% <ø> (ø)
src/lib.rs	16.51% <50.00%> (-0.09%)	⬇️
src/cookies/interceptor.rs	86.84% <94.44%> (+12.92%)	⬆️
src/client.rs	82.24% <97.22%> (-0.11%)	⬇️
src/default_headers.rs	100.00% <100.00%> (ø)
src/interceptor/context.rs	75.00% <100.00%> (ø)
src/interceptor/obj.rs	100.00% <100.00%> (ø)
src/redirect.rs	86.77% <100.00%> (+8.41%)	⬆️
... and 3 more

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[Xuanwo]

Hi, @sagebind, can you take a look into this PR? Thanks!

[Xuanwo]

@sagebind I did some refactor on this PR, PTAL

[sagebind]

Apologies for my prolonged absence, this looks fantastic! Thanks so much for your work on this.