pack/unpack optional bigint support

[Speedy37]

No description provided.

[github-actions]

Pull Request Test Coverage Report for Build 4147edb273bb1d609adb5df69831955394b87207-PR-178

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 71.044%

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Totals
Change from base Build 3f95533b644756c828e100b91e8aee228ec9ded5:	0.02%
Covered Lines:	2348
Relevant Lines:	3305

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💛 - Coveralls

[codecov-io]

Codecov Report

Merging #178 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #178      +/-   ##
==========================================
+ Coverage    83.3%   83.33%   +0.03%     
==========================================
  Files          15       15              
  Lines        2617     2616       -1     
==========================================
  Hits         2180     2180              
+ Misses        437      436       -1

Impacted Files	Coverage Δ
foundationdb/src/tuple/mod.rs	85.92% <ø> (ø)	⬆️
foundationdb/src/tuple/pack.rs	88.4% <100%> (-0.04%)	⬇️
foundationdb-bindingtester/src/main.rs	86.5% <0%> (+0.11%)	⬆️

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