Simplify NoteMetadata constructor by making tag optional

[Copilot]

Summary

This PR implements the change requested in issue #2334 to modify the NoteMetadata constructor API to use a builder pattern.

Changes Made

Constructor Modification

• Modified NoteMetadata::new() to only take sender: AccountId and note_type: NoteType parameters
• The tag now defaults to NoteTag::default() (which is 0)
• This makes the API cleaner and more intuitive for common use cases where a tag is not needed

New Builder Methods

• Added with_tag() builder method to set a custom tag when needed
• Added set_tag() mutator method for setting tags on existing instances
• Improved documentation to clarify the difference between builder and mutator methods

API Usage Comparison

Before:

let metadata = NoteMetadata::new(sender_id, NoteType::Public, tag);

After:

// Without custom tag (uses default)
let metadata = NoteMetadata::new(sender_id, NoteType::Public);

// With custom tag
let metadata = NoteMetadata::new(sender_id, NoteType::Public)
    .with_tag(tag)
    .with_attachment(attachment);

Updated Call Sites

Updated ~40 call sites across all crates:

• ✅ miden-protocol (4 instances)
• ✅ miden-testing (19 instances)
• ✅ miden-standards (10 instances)
• ✅ miden-tx (1 instance)
• ✅ miden-agglayer (1 instance)

Testing

• ✅ All unit tests pass
• ✅ Clippy checks pass with no warnings
• ✅ Code formatting complies with project standards
• ✅ Code review completed and feedback addressed
• ✅ Changelog entry added for PR Simplify NoteMetadata constructor by making tag optional #2384

Security Summary

This change is a pure refactoring that maintains the same behavior but with a cleaner API. No security vulnerabilities were introduced:

• The default tag value (0) is the same as before when tags weren't being used
• All existing functionality is preserved
• The change is backwards compatible at the binary level (serialization/deserialization unchanged)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Change the NoteMetadata constructor not to take the tag by default</issue_title>
<issue_description>Also, maybe we should change the NoteMetadata constructor not to take the tag by default. This way, we'd just do:

let metadata = NoteMetadata::new(sender_account_id, NoteType::Public)
    .with_attachment(attachment);

And in cases when the tag is required, we'd do:

let metadata = NoteMetadata::new(sender_account_id, NoteType::Public)
    .with_tag(tag)
    .with_attachment(attachment);

Originally posted by @bobbinth in #2334 (comment)
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Change the NoteMetadata constructor not to take the tag by default #2383

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[mmagician]

lgtm

[mmagician]

@copilot add changelog entry, the PR number is 2384

[Copilot]

@copilot add changelog entry, the PR number is 2384

Added changelog entry in commit 12a8f8f.

[bobbinth]

nit: I would have maybe changed the parameter type to something like Into<NoteTag>. This way, we'd be able to call this method with anything that can be trivially converted into a NoteTag (would make testing code a bit easier).