analysis: fix namespace parsing after Yojson migration

[fhammerschmidt]

@aspeddro

Problem

The Yojson migration changed analysis config parsing in a subtle way. The code
used Yojson.Safe.Util.to_string_option and to_bool_option as if they were
non-throwing type probes, but Yojson's _option helpers only return None for
null; they still raise Type_error for other mismatched JSON types.

That broke valid namespace configs such as:

{ "namespace": "my-namespace" }

because analysis first tried to decode namespace as a string, then also tried
to decode it as a bool. The second probe raised instead of returning None.
The opposite shape, { "namespace": true }, had the same problem in reverse.

Fix

Parse namespace once into a closed OCaml variant:

type namespace_config =
  | NamespaceDisabled
  | NamespaceFromPackageName
  | NamespaceExplicit of string

Then derive the existing string option from that typed representation. This
makes the bool/string/absent cases exhaustive and prevents later code from
probing the same raw JSON value as multiple incompatible types.

The patch also adds shared non-throwing Yojson helpers for config-style reads
and replaces the remaining unsafe Yojson option extractors in analysis and
reanalyze's .sourcedirs.json scan-plan parsing.

Coverage

Added OUnit coverage for namespace config parsing:

• absent namespace
• namespace: false
• invalid non-string/non-bool values
• namespace: true
• explicit string namespace

[codecov]

Codecov Report

❌ Patch coverage is 91.37931% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.68%. Comparing base (f390dfc) to head (32f0ddb).

Files with missing lines	Patch %	Lines
analysis/src/FindFiles.ml	75.00%	4 Missing ⚠️
tests/ounit_tests/ounit_analysis_config_tests.ml	97.56%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8454      +/-   ##
==========================================
+ Coverage   60.63%   60.68%   +0.04%     
==========================================
  Files         373      373              
  Lines       54057    54095      +38     
==========================================
+ Hits        32778    32826      +48     
+ Misses      21279    21269      -10     

Files with missing lines	Coverage Δ
analysis/src/Packages.ml	55.14% <100.00%> (ø)
tests/ounit_tests/ounit_tests_main.ml	100.00% <ø> (ø)
tests/ounit_tests/ounit_analysis_config_tests.ml	97.56% <97.56%> (ø)
analysis/src/FindFiles.ml	58.20% <75.00%> (+4.72%)	⬆️

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commit: 32f0ddb

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[cknitt]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Another round soon, please!

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[aspeddro]

Thank you to fix it @fhammerschmidt