[KFilippopolitis]

Exaflow PR #656 (algorithms/t-test-corrections) changes t-test values,
not their shape: one-sided bounds use t_{1-alpha}, p-values come from
the survival function (3.9e-235 instead of 0), a one-row group no
longer nulls the independent t-test, and the paired spec now labels x
"Measurement 1" and y "Measurement 2" (mean_diff = x - y).

Backend fix: results pass through as Exaflow sent them

Results used to be parsed with Gson and written back with Spring's
Jackson. That changed them in two ways:

• Gson turned every number into a double (n_obs: 217 reached the UI as 217.0);
• application.yml's non_null inclusion dropped every null inside a
  result, at any depth (a t-test p: null disappeared).

AnalysisService now returns a 200 body as RawJson, and
ExperimentDTO serves a stored result as RawJson. Jackson 2
(JsonConverters, storing a kept run) and Spring's Jackson 3 both write
it unchanged. Exaflow writes results with pydantic model_dump_json,
which emits no bare NaN/Infinity, so the text is always valid JSON.

Breaking: result integers are no longer sent as doubles, and null
fields in results are sent as null instead of being omitted. The UI
reads both forms the same way (toFiniteNumber, first()).

Contract tests

Across a kept run's store-and-serve path:

• the open side of a one-sided CI stays the string "Infinity";
• a tiny p-value keeps its value;
• null statistics stay present as null, and integers stay integers;
• the paired x/y labels and alternative enums reach the UI as sent;
• one-sided run parameters read from UI JSON reach Exaflow unchanged.

ExperimentDTOResultTest checks that a stored result is served with its
nulls (nested too) and integers; it fails on the old Gson path.
SpringJsonMapper (test) builds the mapper Spring MVC uses from
application.yml. PR #39 adds the identical file, so either merge order
is clean.

Merge notes

• Conflicts with fix(analysis): map Exaflow 503 and 413 to user-facing errors #42 on two adjacent lines in AnalysisService.convertResponseToAnalysisResult.
  Resolve by keeping both: case 200 -> new RawJson(...) from this PR,
  and the 413/503 cases from fix(analysis): map Exaflow 503 and 413 to user-facing errors #42.
• UI counterpart: platform-ui#60.
• Depends on Exaflow PR #656.

Tests

mvn test: 129 tests, 0 failures.