fix: add bigint support to system transfers

[steveluscher]

Note: this PR was made by @konytech, but @steveluscher is an idiot and accidentally corrupted #24797; reopened it as this PR.

Problem

System transfers only support the 'number' type for lamports. For transferring large amounts, supporting 'bigint' like it's done in the spl-token library is required.

This follows the same encoding/decoding approach used by the spl-token library:
https://github.com/solana-labs/solana-program-library/blob/master/token/js/src/instructions/transfer.ts#L56

Summary of Changes

• Add bigint support to system transfers
• Add @solana/buffer-layout-utils package required to decode u64 to bigint
• Fix tests with this new type support

[codecov]

Codecov Report

Merging #24975 (1dd345a) into master (eae9a66) will decrease coverage by 6.8%.
The diff coverage is n/a.

❗ Current head 1dd345a differs from pull request most recent head 9a02b52. Consider uploading reports for the commit 9a02b52 to get more accurate results

@@             Coverage Diff             @@
##           master   #24975       +/-   ##
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- Coverage    82.0%    75.1%     -6.9%     
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  Files         598       38      -560     
  Lines      165953     2244   -163709     
  Branches        0      323      +323     
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- Hits       136170     1687   -134483     
+ Misses      29783      444    -29339     
- Partials        0      113      +113     

[steveluscher]

@jordansexton, are you OK with this?

bigint support (relatively bad in Safari; click ‘date relative’): https://caniuse.com/bigint

Only other thing I could do would be to write a layout adapter for BN (ie. bn.js, the BigNum polyfill`).

[jordaaash]

Yep, fine with this. Last 1 or 2 version support is pretty typical for crypto libs.

[konytech]

Thanks for taking care of this @steveluscher