util: bigint bytes fixes

[gabrocheleau]

This PR:

• fixes Improve BigInt<>Bytes conversion helpers test coverage & address edge case issues #3180
• fixes Mutation bug in bytesToBigInt #4202

Summary of the decisions and rationale (relevant with regards to our previous discussion on #3180 @jochem-brouwer )

• bigIntToBytes(0n)

  • Keep returning [0].
  • Use bigIntToUnpaddedBytes when an empty array is desired.
  • [0] = “the number zero”, [] = “empty/absence”; semantically distinct and encoded differently in RLP.

• setLengthLeft truncation behavior

  • Default: throw if truncation would occur.
  • Add an explicit allowTruncate option to opt into truncation.
  • A padding helper should not silently lose data; callers must explicitly choose left vs right truncation.

• bytesToBigInt([])

  • Keep returning 0n.
  • Treat empty bytes as zero and preserve roundtrips with bigIntToUnpaddedBytes.

• Runtime type checks

  • Add an assertIsBytes() helper (checking instanceof Uint8Array) and use it in bytesToBigInt and other bytes-accepting functions.

• Mutation bug in bytesToBigInt

  • Fix by using .slice().reverse() instead of .reverse() directly on the input.

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.58%. Comparing base (0430b7e) to head (09c1562).

Additional details and impacted files

Flag	Coverage Δ
block	88.44% <ø> (ø)
blockchain	88.85% <ø> (ø)
common	93.38% <ø> (ø)
evm	62.01% <ø> (ø)
mpt	90.11% <ø> (ø)
statemanager	78.10% <ø> (ø)
static	91.35% <ø> (ø)
tx	88.01% <ø> (ø)
util	85.07% <91.66%> (+0.12%)	⬆️
vm	65.08% <ø> (ø)

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[github-actions]

📦 Bundle Size Analysis

Package	Size (gzip)	Δ
binarytree	30.1 KB	⚪ ±0%
block	45.4 KB	⚪ ±0%
blockchain	52.4 KB	⚪ ±0%
client	181.7 KB	⚪ ±0%
common	44.9 KB	⚪ ±0%
devp2p	76.4 KB	⚪ ±0%
e2store	30.3 KB	⚪ ±0%
ethash	8.4 KB	⚪ ±0%
evm	201.4 KB	⚪ ±0%
genesis	519.5 KB	⚪ ±0%
mpt	55.1 KB	⚪ ±0%
rlp	7.2 KB	⚪ ±0%
statemanager	57.2 KB	⚪ ±0%
testdata	60.2 KB	⚪ ±0%
tx	87.0 KB	⚪ ±0%
util	62.1 KB	🔴 +0.3 KB (+0.44%)
vm	61.3 KB	⚪ ±0%
wallet	14.0 KB	⚪ ±0%

_{Generated by bundle-size workflow}