build: upgrade to typescript 6

[joker23]

This PR will update all of the configuration files (package.json, jest.config.js, and tsconfig.json) to use typescript 6.

There shouldn't be any implementation changes here as all implementation at this point should conform nicely with the new typescript version.

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Note

Medium Risk
Wide toolchain change across every package can alter emitted declarations, module resolution, and CI check/build behavior even without application code edits; verify full monorepo build and tests.

Overview
Upgrades the monorepo from TypeScript 5.1.6 to 6.0.3 across the root and workspace packages, with matching updates to Jest/ts-jest and tsconfig settings so tsc, tests, and bundlers still work under TS 6.

Compiler config is adjusted for TS 6 defaults and stricter resolution: moduleResolution moves from legacy node to bundler (most browser/edge/tsup packages) or node16 (Node CJS packages like server-node, stores, and several examples). Several packages switch module from commonjs to ESNext or node16, bump lib toward es2020, and add ignoreDeprecations: "6.0" where needed. Explicit types for Jest/Node are added in many tsconfigs.

Jest: root jest.config.js configures ts-jest with module: 'CommonJS' for tests. Package jest configs are mostly reformatted; React-related jest ts-jest options are simplified.

Build tooling: React SDK adds tsconfig.build.json (extends main config with deprecation ignores) and points tsup at it for DTS generation. Shopify Oxygen contract-tests set tsup dts: false. Server-AI example tsconfigs gain rootDir/outDir and bundler resolution. The hello-react example bumps @types/react / @types/react-dom to v19.

^{Reviewed by Cursor Bugbot for commit 462a5a2. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

@launchdarkly/js-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 26365 bytes
Compressed size limit: 29000
Uncompressed size: 129044 bytes

[github-actions]

@launchdarkly/browser size report
This is the brotli compressed size of the ESM build.
Compressed size: 179579 bytes
Compressed size limit: 200000
Uncompressed size: 831422 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
Compressed size: 31978 bytes
Compressed size limit: 34000
Uncompressed size: 114243 bytes

[github-actions]

@launchdarkly/js-client-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 38756 bytes
Compressed size limit: 39000
Uncompressed size: 212356 bytes

[joker23]

@cursor review

[cursor]

✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit 462a5a2. Configure here.}