fix: add missing package subpath entrypoints - #72

Summary

• add the missing core, memory, and policies source entrypoints that are already declared as package subpath exports
• use explicit .js relative imports in the new ESM entrypoints and memory provider import chain so the packed package can load in Node ESM consumers

Why

The published package advertises these subpaths:

• @juspay-jaf/jaf/core
• @juspay-jaf/jaf/memory
• @juspay-jaf/jaf/policies

but @juspay-jaf/jaf@0.1.46 does not ship dist/core/index.js, dist/memory/index.js, or dist/policies/index.js, so clean consumer imports fail with ERR_MODULE_NOT_FOUND.

Validation

• corepack pnpm run build
• corepack pnpm run typecheck
• corepack pnpm run lint
• git diff --check
• packed the fixed checkout with npm pack --pack-destination ... --json --ignore-scripts
• installed the packed tarball in a clean temp consumer and verified:
  • import('@juspay-jaf/jaf/core')
  • import('@juspay-jaf/jaf/memory')
  • import('@juspay-jaf/jaf/policies')

I also reproduced the current published-package failure in a clean temp consumer before this patch.