feat!: Remove all uses of CJS, add named Flagsmith export

[rolodato]

The current beta version of this library doesn't work when used from ESM:

// test.mjs
import Flagsmith, { EnvironmentModel } from "./build/esm/index.js"
console.log(Flagsmith, EnvironmentModel)

% node index.mjs
file:///Users/rolodato/source/flagsmith/flagsmith-nodejs-client/test/node_modules/flagsmith-nodejs/build/esm/flagsmith-engine/identities/models.js:2
const { v4: uuidv4 } = require('uuid');
                       ^

ReferenceError: require is not defined in ES module scope, you can use import instead
    at file:///Users/rolodato/source/flagsmith/flagsmith-nodejs-client/test/node_modules/flagsmith-nodejs/build/esm/flagsmith-engine/identities/models.js:2:24
    at ModuleJob.run (node:internal/modules/esm/module_job:195:25)
    at async ModuleLoader.import (node:internal/modules/esm/loader:337:24)
    at async loadESM (node:internal/process/esm_loader:34:7)
    at async handleMainPromise (node:internal/modules/run_main:106:12)

Removing this use of require reveals another use of module.exports, which is CJS and does not get compiled:

% node test.mjs
file:///Users/rolodato/source/flagsmith/flagsmith-nodejs-client/build/esm/index.js:4
module.exports = Flagsmith;
^

ReferenceError: module is not defined in ES module scope
    at file:///Users/rolodato/source/flagsmith/flagsmith-nodejs-client/build/esm/index.js:4:1
    at ModuleJob.run (node:internal/modules/esm/module_job:195:25)
    at async ModuleLoader.import (node:internal/modules/esm/loader:337:24)
    at async loadESM (node:internal/process/esm_loader:34:7)
    at async handleMainPromise (node:internal/modules/run_main:106:12)

Fixing this makes everything work:

% node test.mjs 
[class Flagsmith] [class EnvironmentModel]

As a bonus, we can add Flagsmith as a named export, for consistency:

// test-default.mjs
import { Flagsmith, EnvironmentModel } from "./build/esm/index.js"
console.log(Flagsmith, EnvironmentModel)

% node test-default.mjs 
[class Flagsmith] [class EnvironmentModel]

Important: this is a breaking change for CJS users, as require now returns an object instead of the Flagsmith class:

> require('./build/cjs/index.js')
{
  AnalyticsProcessor: [Getter],
  FlagsmithAPIError: [Getter],
  FlagsmithClientError: [Getter],
  EnvironmentDataPollingManager: [Getter],
  DefaultFlag: [Getter],
[...]

This PR also has some QoL changes:

• 6c1d1b9 removes esModuleInterop - compiled code doesn't change, but this makes the code truly ESM-only
• 4cc7097, a9e9e6c replace deps with built-in Node functions - this makes the test suite take ~4 seconds vs ~120 previously
• 8eb2703 upgrade GHA workflow - this makes the CI run take ~17s vs ~3m previously

[matthewelwell]

Looks great to me. One main question about a possible breaking change that wasn't listed in the description. Once that's understood, I think we can move forward and get this released.

[rolodato]

Bonus - hashing is now over 100x faster

Index: tests/engine/unit/utils/utils.bench.ts
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/tests/engine/unit/utils/utils.bench.ts b/tests/engine/unit/utils/utils.bench.ts
new file mode 100644
--- /dev/null	(date 1730987845619)
+++ b/tests/engine/unit/utils/utils.bench.ts	(date 1730987845619)
@@ -0,0 +1,17 @@
+import {bench} from "vitest";
+import {
+    getHashedPercentateForObjIds,
+    getHashedPercentateForObjIdsOld
+} from "../../../../flagsmith-engine/utils/hashing/index.js";
+import {randomUUID as uuidv4} from "crypto";
+
+bench('old hashing', () => {
+    const _ = getHashedPercentateForObjIdsOld([uuidv4()])
+}, {
+    signal: AbortSignal.timeout(10000)
+})
+bench('new hashing', () => {
+    const _ = getHashedPercentateForObjIds([uuidv4()])
+}, {
+    signal: AbortSignal.timeout(10000)
+})

% npx vitest bench
Benchmarking is an experimental feature.
Breaking changes might not follow SemVer, please pin Vitest's version when using it.

 DEV  v2.1.2 /Users/rolodato/source/flagsmith/flagsmith-nodejs-client

 ✓ tests/engine/unit/utils/utils.bench.ts (2) 1303ms
     name                 hz     min     max    mean     p75     p99    p995    p999     rme  samples
   · old hashing    4,372.66  0.1842  0.3767  0.2287  0.2331  0.3018  0.3185  0.3650  ±0.39%     2187
   · new hashing  578,653.03  0.0014  1.3175  0.0017  0.0016  0.0028  0.0030  0.0053  ±1.63%   289327   fastest


 BENCH  Summary

  new hashing - tests/engine/unit/utils/utils.bench.ts
    132.33x faster than old hashing