Apply channels.filters at read time (#103)

[tombonfert]

Summary

SolverConfig.channels accepted a filters dict but the engine never applied it, so channel-table filters were silently dropped. This wires them up and adds a guardrail against the one way the feature can be misused.

Changes

• Apply channels.filters in DefaultSolver._prepare_channels_join, after column_name_mapping and before the UDF-column projection, using the same equality-filter mechanism as container_tags, container_metrics, and channel_mapping. Applying it before the projection lets a filter reference any channels column, including dimension columns the solve step drops.
• Reject implausibility-via-filter in RAW mode. A new config validator raises when data_type = RAW and channels.filters targets is_plausible. Such a filter runs before raw encoding and would bridge intervals across dropped samples; drop_implausible_data is the correct tool (it drops inside the encoder, so boundaries stay correct). The check keys off the internal is_plausible name, so it also catches a physical column mapped to it.
• Docs. Documented channels-table filter support, noted that filter values are coerced to the target column type (booleans take "true"/"false"), added the previously undocumented is_plausible and timestamp internal names to the mapping table, and added a RAW-mode caveat. Also corrected a stale "RAW to RLE" error string to "RAW to interval" (the drop works for both raw encoders).
• Solves Apply solver_config.channels.filters when reading the channels table #103

Test Plan

• Unit tests added/updated
• Manual testing completed
• Documentation updated (if applicable)

Checklist

• Code follows project style guidelines
• Self-review completed
• No new linter warnings introduced

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.80%. Comparing base (88af4a7) to head (8196245).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #104      +/-   ##
==========================================
+ Coverage   89.78%   89.80%   +0.01%     
==========================================
  Files          62       62              
  Lines        5717     5726       +9     
  Branches      716      719       +3     
==========================================
+ Hits         5133     5142       +9     
  Misses        463      463              
  Partials      121      121              

Flag	Coverage Δ
query_engine	86.12% <100.00%> (+<0.01%)	⬆️
reporting	94.67% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ery_engine/analyze/query/solvers/default_solver.py	94.86% <100.00%> (+0.02%)	⬆️
src/impulse_reporting/config/config_parser.py	97.46% <100.00%> (+0.09%)	⬆️

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