Format persistence keys with the invariant culture [patch]

[matt-edmondson]

Fixes #46

What changed

FileSystemPersistenceProvider and TempPersistenceProvider built file names with key.ToString(), which uses the current culture. GetAllKeysAsync then parsed those names back with the invariant culture. Under de-DE, that caused two problems:

• A double key 1.5 was stored as 1,5.json and listed back as 15.
• A DateTime key came back with its day and month swapped.

Data written under one culture also could not be found under another.

• New PersistenceProviderUtilities.FormatKey<TKey>. This is the one helper both providers now use to turn a key into its file-name text, so the two cannot drift apart:
  • double/float use the round-trip "R" format.
  • DateTime/DateTimeOffset use ISO 8601 "O".
  • Other IFormattable types format with the invariant culture.
  • Strings pass through unchanged.
• TryConvertToKey now parses DateTime with DateTimeStyles.RoundtripKind, so a UTC key is not converted to local time on the way back. It also parses DateTimeOffset, which Convert.ChangeType cannot convert at all.

Compatibility note

Release note: files written before this change under a culture that differs from invariant keep their old names, and the new format will not find them. For example, a 1,5.json written under de-DE.

DateTime keys are also named differently now, in every culture. The old name was a culture-specific short date with seconds precision; the new one is the ISO 8601 round-trip form. String, integer and GUID keys are unaffected. Under invariant-like cultures, double keys are unaffected too, because .NET's default double.ToString() is already the shortest round-trippable form.

The triage suggested a fallback lookup or a release note. I went with the note, because a fallback would have to cover Exists, Retrieve, Remove and enumeration in both providers.

Tests

In PersistenceNamingTests:

• FileSystem_Double_And_Date_Keys_Round_Trip_Across_Cultures and Temp_Double_And_Date_Keys_Round_Trip_Across_Cultures each:
  1. store double and DateTime keys under a comma-decimal, day-first culture
  2. assert that GetAllKeysAsync returns exactly those keys
  3. switch to a month-first, twelve-hour culture and assert that RetrieveAsync still finds each one
• FormatKey_Ignores_The_Current_Culture pins the formatted text.

The test cultures are cloned from the invariant culture rather than built with new CultureInfo("de-DE"), so the tests also run on machines in globalization-invariant mode with no ICU data. This container is one of those.

Verification

• With the provider and TryConvertToKey changes reverted (keeping only FormatKey so the tests compile), both round-trip tests fail: the expected key 1,5 is missing from the listed keys.
• With the change, the full suite passes: 922 of 922 on net10.0.
• Essentials and both providers build for every target, including netstandard2.1, with 0 warnings.

🤖 Generated with Claude Code

https://claude.ai/code/session_01CzC1o7LFYHYaoWmVy1NLcp

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Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

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