normalize MessageId filters for event subscriptions

[raja-gade]

Allow MessageIds to be specified with or without registry prefixes and store them in fully-qualified form for consistent event filtering.

Always cache the Redfish event log file on watcher startup.

Test:
Redfish Event subscription is working fine for the subscribed MessageIDs

[supven01]

@copilot - Can you review changes?

[Copilot]

@copilot - Can you review changes?

Here is my review of the changes in this PR:

redfish-core/lib/event_service.hpp

✅ The <format> header is correctly added since std::format is now used.

✅ Core fix: Previously, bare message keys like "PostComplete" were stored as-is, but eventMatchesFilter() always looks for "Registry.MessageKey" format (e.g., "OpenBMC.PostComplete"). This caused MessageId filtering to silently fail for all subscriptions. The change fixes this by normalizing before storing.

✅ Both input formats are correctly handled:

• Bare key: "PostComplete" → stored as "OpenBMC.PostComplete"
• Prefixed key: "OpenBMC.PostComplete" → stored as "OpenBMC.PostComplete"

✅ The break after adding to qualifiedMsgIds correctly prevents duplicate entries if the same message key appears in multiple registries.

⚠️ Minor: The else branch at line 643 (registryPrefix = subValue->userSub->registryPrefixes) is unreachable when processing MessageIds, because the validation at line 375-383 already enforces that RegistryPrefixes and MessageIds cannot both be non-empty in the same request.

⚠️ Note: Full 4-part Redfish MessageId format ("OpenBMC.0.1.PostComplete") is not handled — the first dot split would give idMsgKey = "0.1.PostComplete" which won't match registry entries. This is a pre-existing limitation (original code also didn't support it), so not a regression.

⚠️ Persisted data: Existing subscriptions stored on disk with old bare-key format will not be re-normalized on load and will continue to have non-matching MessageIds. Since the original code was already broken for this case, it is not a regression. For production deployments, subscriptions would need to be recreated after this update.

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redfish-core/src/filesystem_log_watcher.cpp

✅ Correct: Removing the if (redfishLogFilePosition != 0) guard and always calling cacheRedfishLogFile() on startup prevents historical log entries from being replayed as new events to subscribers when bmcweb restarts. This is the right behavior.

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Overall: The changes are correct and fix a real bug where MessageId filtering was silently not working. No critical issues identified.

[raja-gade]

@copilot - Can you review changes?

Addressed the feedback from copilot