feat: add BigIntField

[wschurman]

Why

Noticed by @FiberJW in https://github.com/expo/universe/pull/10420#discussion_r953010810. Knex (node-postgres) represents the BIGINT type as a string, so using IntField is incorrect.

How

This fixes that by adding a BigInt field that is of string type.

Test Plan

Run new test case.

[codecov]

Codecov Report

Merging #193 (31f03da) into main (8bdd9f7) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #193   +/-   ##
=======================================
  Coverage   96.29%   96.30%           
=======================================
  Files          80       81    +1     
  Lines        2024     2029    +5     
  Branches      269      269           
=======================================
+ Hits         1949     1954    +5     
  Misses         70       70           
  Partials        5        5           

Flag	Coverage Δ
integration	96.30% <100.00%> (+<0.01%)	⬆️
unittest	96.30% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packages/entity/src/EntityFields.ts	100.00% <ø> (ø)
...s/entity-database-adapter-knex/src/EntityFields.ts	100.00% <100.00%> (ø)
...-adapter-knex/src/PostgresEntityDatabaseAdapter.ts	100.00% <100.00%> (ø)

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[FiberJW]

This looks good to me! Thanks for updating the library to support my GitHub integration work!