[PWGJE] Clean up EMCALClusters header and add `getClusterDefinitionFr…

[mhemmer-cern]

…omString` function

• Add Default value for algorithm of EMCALClusterDefinition
• Update constructor with member initilizer
• Add new function getClusterDefinitionFromID to obtain the cluster definition via the storage ID
• Change function getClusterDefinitionFromString to use an unordered_map<std::string,int> instead of multiple if statements with string comparison
• Rename ClusterAlgorithm_t to ClusterAlgorithm to fit naming conventions
• Return type of both functions to get the ClusterDefinition is now const EMCALClusterDefinition&, was const EMCALClusterDefinition before (not a reference but a copy)
• Add inline to the different EMCALClusterDefinition definitions to ensure they are only in memory ONCE and not per file that includes them.

[github-actions]

O2 linter results: ❌ 5 errors, ⚠️ 1 warnings, 🔕 0 disabled

[alibuild]

Error while checking build/O2Physics/o2 for 94f1295 at 2026-09-09 15:47:

## sw/BUILD/O2Physics-latest/log
c++: fatal error: Killed signal terminated program cc1plus
ninja: build stopped: subcommand failed.

Full log here.

[fjonasALICE]

assuming build issue is transient, everything looks good to me! Most critical is probably renaming of ClusterAlgorithm_t to ClusterAlgorithm, but i did not find anything else in O2 and O2Physics that breaks due to this renaming

[mhemmer-cern]

assuming build issue is transient, everything looks good to me! Most critical is probably renaming of ClusterAlgorithm_t to ClusterAlgorithm, but i did not find anything else in O2 and O2Physics that breaks due to this renaming

I also checked for ClusterAlgorithm_t in the whole AliceO2Group to make sure it wasn't used somewhere else. So this renaming should be fine.

[alibuild]

Auto-approving on behalf of @mhemmer-cern.