feat(aztec)!: add counter template for aztec init

[nchamo]

Why we are doing this

The default project scaffolded by aztec init was too minimal -- it created a blank contract with no callable functions, making it hard for new developers to understand how Aztec contracts work.

How it worked before

• aztec init created a workspace with a blank contract (empty impl block) and a basic test
• aztec new <name> created the same blank contract, either as a new project or adding to an existing workspace

What changes

• aztec new stays the same -- it scaffolds a blank contract, either as a new standalone project or as a new crate added to an existing workspace
• aztec init now scaffolds a Counter example with:
  • A private counter contract using Owned<BalanceSet> for encrypted state
  • Annotated functions (constructor, increment, get_counter) with short docs explaining privacy model and execution context
  • A test suite covering constructor initialization and increment

Technical details

We used to build the blank project directly from the bash script. Now we have templates we can simply copy, instead of containing the entire code inside the .sh file

What doesn't change

The existing Counter tutorial docs remain valid since they use aztec new, which still scaffolds the blank template.

Feedback wanted

Please let me know if you have any suggestions on the template content, comments or anything else.

Fixes F-581

[critesjosh]

it might be worth clarifying that "ownership" is achieved via readability (encryption) rather than access control (e.g. "Owned dictates who will receive the encrypted notes")

[nchamo]

You are right, definitely worth mentioning

[dbanks12]

LGTM once @critesjosh and others are happy!