feat: add mapping names to Flamegraph

[elizaveta-andreeva]

Summary

Adds filename/mapping information to the Flamegraph response, enabling Grafana to apply custom coloring schemes based on kernel/user space symbols. The mapping data exposes the executable for each symbol, allowing Grafana to identify which binary or library a frame belongs to.

Changes

Proto changes:

• Add mapping_names field ([]string) to FlameGraph and TreeReport proto messages
• Add mapping field (map<function_name, filename>) to SelectMergeStacktracesResponse and SelectMergeSpanProfileResponse proto messages

Resolver:

• Add TreeWithMappings() method to Resolver that builds a function name -> filename mapping from symbol data

FlameGraph construction:

• Populate mapping_names in NewFlameGraph() using the mapping built above
• Propagate mapping through the query path: queryTree -> TreeReport -> SelectMergeStacktracesResponse / SelectMergeSpanProfileResponse

pprof / OTLP:

• Add buildMappingFromPprof() and buildMappingFromProfile() helpers to extract mapping from pprof profiles (pprof -> profile -> mapping)
• Use frameType to distinguish user vs. kernel space symbols when converting OTLP to Google profile format
• Add [kernel] prefix to kernel symbol mapping filenames during OTLP conversion, so that Grafana can correctly classify and color kernel frames

Tests:

• Add unit tests covering the new mapping logic

Related PR: grafana/grafana#125627

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[elizaveta-andreeva]

@korniltsev-grafanista could you take a look pls?