tests(ext/node): Port buffer_test.ts from deno_std

[fbaltor]

This PR port all the tests from deno_std concerning the Node.js Buffer class, improving the coverage of the task #17840.

[Hootner]

Here's a brief overview of the test cases presented in the code:

Test Buffer readUIntLE:
This test is checking if the readUIntLE (read Unsigned Int Little Endian) function is working as expected by reading 1-byte, 2-byte, and 4-byte values from a buffer.

Test Buffer copy works as expected:
This test verifies that a buffer copy operation indeed adds a certain target buffer's contents to another buffer and that it reflects the same content changes in the source object.

Test Buffer copy respects the starting point for copy:
This test checks that the copy operation appropriately respects the specified starting point for the copy.

Test Buffer copy doesn't throw on offset but copies until offset reached:
This test ensures that the copy operation does not throw an error if the specified offset is reached but instead actually copies the contents until the offset is reached.

Test Buffer from string creates a Buffer:
This test checks if creating a Buffer from a string works as expected, both in terms of buffer size and content.

Test Buffer from string hex/base64 and Buffer to string hex/base64:
These tests validate that when creating Buffers from strings in different encodings (hex, base64), the resultant Buffers have the appropriate size and content. Similar checks are done when converting Buffers to strings in these encodings.

Test Buffer from string invalid encoding:
This test ensures that a default "utf8" encoding is used when an invalid or unspecified encoding is provided.

Test Buffer from another buffer creates a Buffer:
This test checks if creating a Buffer from another Buffer works as intended.

Test isBuffer returns true/false:
These tests validate that the static function "isBuffer" accurately detects whether an object is a Buffer or not.

Test Buffer toJSON:
This test verifies that a Buffer can be successfully converted to a JSON object.

Test slice does not create a copy:
This test demonstrates that the slice method applied to a Buffer doesn't create a copy.

Test slice with infinity returns empty buffer:
This test checks if slicing a Buffer with the end value set to Infinity returns an empty Buffer.

Test isEncoding returns true/false:
These tests check if the static function "isEncoding" accurately identifies valid/invalid encodings.

Test utf8Write handle missing optional length argument:
This test ensures that the utf8Write function works correctly even when an optional length argument is missing.

If you have any questions about specific test cases, feel free to ask!

[kt3k]

LGTM. Thanks!