feat: adds types and tests for lexicographic-integer (#41025)

Signed-off-by: Carson Farmer <carson.farmer@gmail.com>

types/lexicographic-integer/index.d.ts

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+// Type definitions for lexicographic-integer 1.1
+// Project: https://github.com/substack/lexicographic-integer
+// Definitions by: Carson Farmer <https://github.com/me>
+// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+
+/**
+ * Return an array of byte values or a lexicographic hex string for an input integer.
+ * @param n The input integer as a javascript number.
+ * @param enc The encoding to use. Can be one of 'array' (default) or 'hex'.
+ */
+export function pack<T extends 'hex' | 'array' = 'array'>(n: number, enc?: T): T extends 'hex' ? string : T extends 'array' ? number[] : never;
+/**
+ * Convert an array of bytes returned by .pack() back into the original javascript number.
+ * @param xs An array of bytes or a hex string.
+ */
+export function unpack(xs: number[] | string): number;

types/lexicographic-integer/lexicographic-integer-tests.ts

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+import { pack, unpack } from 'lexicographic-integer';
+
+const a = 1e55;
+const b = 1.0000000000001e55;
+const ha = pack(a, 'hex');
+const hb = pack(b, 'hex');
+console.log(ha, hb);
+
+const num = 555;
+const encoded = pack(num, 'hex');
+const decoded1: number = unpack(encoded);
+console.log(decoded1);
+
+let prev: string | number[] = pack(0);
+let n: number;
+let skip = 1;
+for (n = 1; n < Number.MAX_VALUE; n += skip) {
+    const cur = pack(n, 'hex');
+    if (cur <= prev.toString()) break;
+    prev = cur;
+    skip = 1 + Math.pow(245, Math.ceil(Math.log(n) / Math.log(256)));
+}
+console.log(n === Infinity);
+
+const decoded2: number = unpack(prev);
+console.log(decoded2);

types/lexicographic-integer/tsconfig.json

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+{
+    "compilerOptions": {
+        "module": "commonjs",
+        "lib": [
+            "es6",
+            "dom"
+        ],
+        "noImplicitAny": true,
+        "noImplicitThis": true,
+        "strictFunctionTypes": true,
+        "strictNullChecks": true,
+        "baseUrl": "../",
+        "typeRoots": [
+            "../"
+        ],
+        "types": [],
+        "noEmit": true,
+        "forceConsistentCasingInFileNames": true
+    },
+    "files": [
+        "index.d.ts",
+        "lexicographic-integer-tests.ts"
+    ]
+}

types/lexicographic-integer/tslint.json

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+{ "extends": "dtslint/dt.json" }