feat: replace npm with pnpm for package management and update depende…

[alismx]

Changes Proposed

• This PR updates the instructions in the README file to use pnpm instead of npm for installing dependencies and for running the build script. This is a more efficient package manager that can also respect pnpm-lock.yaml which is added in this PR for more deterministic builds.
• It also introduces a change in package management by adding pnpm-lock.yaml file and removes the package-lock.json file, which corresponds to npm. This enforces pnpm usage for future use.

Additional Information

• Porting to pnpm from npm is a conscious decision owing to its efficient installation process and better disk usage.
• Future updates should continue to use pnpm for any addition/removal/updation of dependencies.

Testing

• Reviewers can validate this PR by pulling the branch locally, running pnpm install to install the dependencies and pnpm run build to execute the build script, as detailed in the updated README. They should run without errors and have the expected outcomes. If they haven't installed pnpm, they need to do that first by running npm install -g pnpm.

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