Bigint silent truncation

[Ryang-21]

What

This fixes silent truncation that occurred when encoding LargeInt by checking that the bytes to be encoded are of the appropriate size. This is necessary as the BigInt.asUintN and BigInt.asintN methods truncate the higher bits when they exceed the provided size param given to the function.

Validation

Tests were added to check functionality at the max and min bounds of the sized integer. Values that are beyond the bounds were tested to throw.

[quietbits]

I'm not super familiar with this repo, but the update looks OK to me.

[Copilot]

Pull request overview

This PR addresses silent truncation when encoding/constructing LargeInt-backed integers by introducing explicit range checks (instead of relying on BigInt.asUintN/asIntN, which truncate) and expanding unit coverage around overflow/underflow behavior.

Changes:

• Tighten LargeInt read/write + isValid to respect signedness and enforce [MIN_VALUE, MAX_VALUE].
• Update bigint assembly logic to validate slice inputs (preventing per-slice truncation) and to fast-fail on single-value overflow/underflow.
• Add unit tests for overflow/underflow for Hyper/UnsignedHyper, and add a new 128-bit LargeInt test suite.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/large-int.js	Read/write paths updated to handle signed 64-bit reads correctly and to enforce range checks; isValid now validates range.
src/bigint-encoder.js	Adds single-value bounds validation and slice-fit assertions to prevent silent truncation during assembly.
test/unit/bigint-encoder_test.js	Adds tests for slice overflow/underflow and exact boundary acceptance.
test/unit/hyper_test.js	Adds overflow/underflow construction tests for signed 64-bit Hyper.
test/unit/unsigned-hyper_test.js	Adds overflow/underflow construction tests for unsigned 64-bit UnsignedHyper.
test/unit/large-int-128_test.js	New coverage for >64-bit LargeInt paths including construction, read/write, and isValid.
CHANGELOG.md	Documents the truncation fix in Unreleased notes (but see review comments re: accuracy/formatting).

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