[19.0][IMP] partner_email_check: clearer duplicate-email message + multi-company scope option

[cliffkujala]

Summary

This improves the duplicate-email handling of partner_email_check in two ways: a clearer, access-aware error message, and a new option to scope uniqueness per company instead of globally.

Clearer, access-aware duplicate message

The duplicate check is an @api.constrains, which always runs as superuser, so uniqueness was (and still is) enforced across all records regardless of the acting user's record rules. Previously a collision raised a generic Email 'x@y.com' is already in use., which is confusing when the user cannot see the conflicting partner (record rules / multi-company): they are blocked from using an address that appears nowhere they can look.

After detecting a conflict, the constraint now re-checks whether the acting user can actually read the conflicting record (self.sudo(False)) and tailors the message:

• Readable → identifies the record so the user can reuse it:
  Email address x@y.com is already in use by <name> (ID: 123). Please input another email address or use the existing record.
• Not readable → explains the block without disclosing the record:
  Email address x@y.com is already in use by a record you do not have access to. Please input a different email address, or contact your system administrator to request access.

Multi-company duplicate scope option

New company setting partner_email_check_duplicate_scope (exposed in Settings, shown only when duplicate filtering is enabled):

• Across all companies (global, default) — unchanged behavior: an address may be used only once in the whole database.
• Within the same company (company) — the same address may be reused by a partner of another company, but must stay unique inside each company (company_id = False is treated as its own bucket).

Compatibility notes

• The new setting defaults to global, preserving the previous behavior.
• The success-path message is now more verbose and, for readable records, discloses the conflicting partner's name and ID (previously a generic string). This is intentional and is the point of the change.

Tests

Adds coverage for: per-company scope allowing the same address in another company, per-company scope still blocking within one company, global scope blocking across companies, and the access-restricted message path (duplicate hidden by a record rule is still blocked, without leaking the record).

[BhaveshHeliconia]

Code and functional review LGTM!

[BhaveshHeliconia]

Suggested change

	"group_ids": [(6, 0, groups.ids)],
	"group_ids": [Commad.set(groups.ids)],

[cliffkujala]

Thanks for the review! Good call on Command.set — much cleaner than the (6, 0, ...) tuple. Small heads-up: the suggestion as written has a typo (Commad.set), so I applied a corrected version manually: added from odoo import Command, switched this line to Command.set(groups.ids), and also converted the ir.rule groups line below to Command.set([]) for consistency. Pushed in the latest commit.