Add Canada VAT rules with province-specific rates

[johngathure]

Summary

Implements Canadian province-specific VAT rates (GST/HST/PST) based on postal code prefixes, addressing issue #9.

pyvat/vat_rules.py — CanadaVatRules

• Added CanadaVatRules class extending NonEuVatRules with full province-level rate logic
• PROVINCE_VAT_RATES maps each postal code prefix (A–Y) to the correct combined rate
• get_vat_rate(item_type, postal_code) resolves rate from the first character of the postal code
• Defaults to Ontario (13 %) when no postal code is provided, as agreed in the issue
• Provinces where we are not registered for provincial tax (Quebec, Manitoba) correctly charge GST only (5 %)
• No B2B exemption — Canadian business customers are taxed identically to consumers

pyvat/region_rules.py — RegionRules / CanadaRegionRules

• Added RegionRules abstract base class to support future region-level rules for other countries (e.g. US states, Swiss cantons)
• CanadaRegionRules exposes get_rate(postal_code) and get_region(postal_code) for consumers that need more than just a rate
• get_region() returns a ProvinceRate (nested NamedTuple) containing the prefix, province name, combined rate, and a tax_types tuple (e.g. (HST,) or (GST, PST)) — useful for rendering invoice line items correctly
• Tax type constants (GST, HST, PST, QST, RST) are scoped to CanadaRegionRules since they are Canada-specific
• Rates are not duplicated — CanadaRegionRules reads directly from CanadaVatRules.PROVINCE_VAT_RATES

setup.py

• Replaced hardcoded packages list with find_packages() so any future sub-packages are picked up automatically without touching setup.py

Provincial rate table

Prefix	Province / Territory	Rate	Tax type
A	Newfoundland and Labrador	15 %	HST
B	Nova Scotia	14 %	HST
C	Prince Edward Island	15 %	HST
E	New Brunswick	15 %	HST
G, H, J	Quebec	5 %	GST only (not registered for QST)
K, L, M, N, P	Ontario	13 %	HST
R	Manitoba	5 %	GST only (not registered for RST)
S	Saskatchewan	11 %	GST + PST
T	Alberta	5 %	GST only
V	British Columbia	12 %	GST + PST
X	Northwest Territories / Nunavut	5 %	GST only
Y	Yukon	5 %	GST only
—	No postal code	13 %	Ontario fallback

Test plan

• Rate returned for every postal code prefix (A–Y)
• Ontario (13 %) fallback when no postal code is provided
• Quebec and Manitoba return 5 % (GST only) — not registered for QST/RST
• B2B transactions charged the same rate as B2C (no exemption)
• Integration with get_sale_vat_charge end-to-end
• Populate gst_number and pst_number registration numbers once available (post-release)
• Update company VAT rates database (post-release, noted in issue)

Related Issues

Closes #9

🤖 Generated with Claude Code

[johngathure]

To release this after review, follow the following steps:

1. Merge into master.
2. Create a release 1.0.4 here.
3. Update Imagify and Monies requirement of pyvat to use the newly created tag on step 2 1.0.4 .

[nicomollet]

⏯️ Merge only after knowing the exact Canadian tax values and follow steps above.

Putting as QA done. QA will be done with Monies.

[nicomollet]

@johngathure Mathieu updated the issue description with the values depending on each Canada state.

1. Update the value for each state and consider the Quebec and Manitoba to be 5%
2. Include a fallback to Ontario value when no postal code (13%)
3. Develop tests for Canada especially:
   • fallback when no postal code
   • state: Quebec, Ontario, British Columbia (we have postal code examples in the issue desc)

⏯️ Make this PR in a ready state and wait for signal for release

[johngathure]

Hi @nicomollet 👋

I've made the changes to use the rates shared by Mathieu and added some tests. Whenever we are ready to QA, I will update monies to use the last commit on this pr, so it picks the newly updated Canadian VAT rates.

[nicomollet]

Approved, let's move to QA in progress until more news in the issue

@johngathure Prepare a PR on Monies side (linked to this issue) matching this (unreleased) version of Pyvat. So that we can eventually deploy to staging for testing.

[nicomollet]

Add update the doc https://www.notion.so/wpmedia/VAT-Tax-rates-Exemption-for-all-countries-2beed22a22f080658719c05700236045 as post release actions please in the PR