feat(schema): log warnings for removeField missing field and invalid HASH path

[linbo328]

Summary

Implemented two warnings requested in the issue:

1. removeField: Logs a warning when the field is not found, including the field name and list of known fields.
2. addField: Logs a warning when a path is provided for HASH storage type.

Changes

• src/schema/schema.ts: Replaced // TODO: log a warning comments with actual console.warn calls.

This helps users diagnose typos in field names when calling removeField.

Closes #13

[banker]

Thanks @linbo328 — appreciate that this covers both #13 and #12 in one PR.

Before merging, could you add unit tests covering both warnings? Suggested cases:

For removeField (closes #13):

• Warning is emitted when removing a field that doesn't exist, and the message includes the field name + the list of known fields.
• Warning includes the empty-state correctly (e.g. Known fields: []) when the schema has no fields.
• No warning is emitted when removing a field that does exist, and the field is actually removed.

For makeField HASH-path (closes #12):

• Warning is emitted when a non-null path is supplied for a HASH-storage field, and the message includes the field name and the path value.
• No warning is emitted when path is null/undefined on HASH storage.
• No warning is emitted on JSON storage where a path is legitimate.

Pattern: use vi.spyOn(console, 'warn').mockImplementation(() => {}) and assert with expect.stringContaining(...) on the message — see tests/unit/schema/schema.test.ts for the existing removeField test pattern, and PR #23 for a worked example of the spy-based assertion style.

Once tests are added I'll re-review and merge.