feat: add options for package manager

[arihantbansal]

• Changes current behavior (require warn, try yarn, warn if yarn is missing, use npm) to using specified package manager (npm, yarn, pnpm) with npm as default fallback if not specified or if specified package manager is missing
• Use package manager option in test scripts too
• Update 'mismatched version' error message to also use specified package manager
  - Adds the package_manager flag in init, build, test, verify, and publish commands.

This PR doesn't change yarn being used to build Anchor itself.

This PR is inspired by #2934, and builds up on it.

Addresses #2881.

[vercel]

@arihantbansal is attempting to deploy a commit to the coral-xyz Team on Vercel.

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[acheroncrypto]

This is a great addition, but I think it would be much better if the package manager could be controlled from Anchor.toml rather than having to pass CLI arguments each time, since this is not something people would want to change too often. For example, we could have something like:

[toolchain]
# Possible values "npm", "yarn" or "pnpm"
package_manager = "npm"

One place where it makes sense to have a CLI option for this is with the init command (because Anchor.toml hasn't been created yet).

[acheroncrypto]

Almost ready. Could you also note this feature in the CHANGELOG?

[acheroncrypto]

Adding a dedicated field for the package manager was already on my to-do list (within a greater refactoring of Anchor.toml), but no reason not to have it now. Thanks!

We'll most likely make npm the default in v0.32 as mentioned earlier.