feat(mint): remove deprecated v0 HTTP API

[b-l-u-e]

Here is what was done for #953 - remove deprecated mint v0 API:

Removed

• cashu/mint/router_deprecated.py - root-level routes (/info, /keys, /mint, /melt, /split, /check, /restore, etc.) that duplicated the old pre-v1 surface.
• tests/mint/test_mint_api_deprecated.py - already fully skipped; removed.
• tests/fuzz/test_fuzz_mint_api_deprecated.py - fuzzing only the removed routes; removed.

Mint app

• cashu/mint/app.py - mounts only the v1 router (no deprecated router). The file on disk already matched this after the edits.

Settings

• debug_mint_only_deprecated removed from cashu/core/settings.py. It only toggled “deprecated-only” vs “v1 + deprecated”; with v0 gone it has no use.

Tests & helpers

• tests/helpers.py - dropped is_deprecated_api_only.
• All tests that branched on debug_mint_only_deprecated / is_deprecated_api_only were simplified (always exercise v1 behavior, or drop obsolete skipif / pytest.skip).
• tests/mint/test_mint_melt.py - skip reason is now “only FakeWallet”; condition is not is_fake only.

CI / docs

• .github/workflows/tests.yml, ci.yml, tests_redis_cache.yml - removed mint-only-deprecated input, matrix dimension, and DEBUG_MINT_ONLY_DEPRECATED env.
• CONTRIBUTING.md - removed the “V0 API only” / DEBUG_MINT_ONLY_DEPRECATED subsection.

Not removed

• Pydantic *_deprecated models in cashu/core/models.py and PostMeltResponse_deprecated usage in cashu/wallet/v1_api.py stay for interoperability with older mint JSON, not for serving the removed routes.

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
202	1	201	21

View the top 1 failed test(s) by shortest run time

::tests.mint.test_mint_melt

Stack Traces | 0s run time

tests/mint/test_mint_melt.py:779: in <module>
    @pytest.mark.skipif(is_deprecated_api_only, reason="Can't run on the deprecated API")
E   NameError: name 'is_deprecated_api_only' is not defined

To view more test analytics, go to the Test Analytics Dashboard
_{📋 Got 3 mins? Take this short survey to help us improve Test Analytics.}

[b-l-u-e]

CI failed tests shows error

tests/mint/test_mint_melt.py:779: in <module>
    @pytest.mark.skipif(is_deprecated_api_only, reason="Can't run on the deprecated API")
E   NameError: name 'is_deprecated_api_only' is not defined

current workspace file ends at line 767 and has no line 779