SDK: Fix toUnits throwing error for values in scientific notation (#8112)

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## PR-Codex overview
This PR enhances the `toUnits` function to handle both scientific notation and fixed-point notation, ensuring accurate conversion of token values with specified decimals. It also adds tests to verify the new functionality.

### Detailed summary
- Modified `toUnits` function to check for scientific notation (e.g., "1e-18").
- Converted scientific notation to fixed-point notation using `Number(tokens).toFixed(decimals)`.
- Added tests for `toUnits` to cover various scientific notation cases, including negative and positive exponents.

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<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

* **New Features**
  * Unit conversion now accepts scientific notation (positive and negative exponents), normalizing values to the configured decimal precision for consistent fixed-point results.

* **Tests**
  * Added comprehensive tests covering positive and negative exponent cases to validate parsing and conversion from scientific notation.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: MananTank

packages/thirdweb/src/utils/units.test.ts

@@ -199,6 +199,19 @@ describe("toUnits", () => {
     expect(toUnits("69.59000000059", 9)).toMatchInlineSnapshot("69590000001n");
     expect(toUnits("69.59000002359", 9)).toMatchInlineSnapshot("69590000024n");
   });
+
+  it("scientific notation", () => {
+    // negative exponents
+    expect(toUnits("1e-18", 18)).toMatchInlineSnapshot("1n");
+    expect(toUnits("1e-16", 18)).toMatchInlineSnapshot("100n");
+    expect(toUnits("1.23456789012345e-7", 18)).toMatchInlineSnapshot(
+      "123456789012n",
+    );
+    // positive exponents
+    expect(toUnits("1.234e3", 18)).toMatchInlineSnapshot(
+      "1234000000000000000000n",
+    );
+  });
 });
 
 describe("toWei", () => {

packages/thirdweb/src/utils/units.ts

@@ -73,6 +73,10 @@ export function toEther(wei: bigint) {
  * @utils
  */
 export function toUnits(tokens: string, decimals: number): bigint {
+  if (tokens.includes("e")) {
+    tokens = Number(tokens).toFixed(decimals);
+  }
+
   let [integerPart, fractionPart = ""] = tokens.split(".") as [string, string];
   const prefix = integerPart.startsWith("-") ? "-" : "";
   if (prefix) {