Fix round-trip conversion for column names with digits after underscores

[Copilot]

Column names like foo_25bar fail to round-trip through field name conversion, producing SQL errors when IHP attempts to reference foo25_bar instead of foo_25bar.

-- Before: broken round-trip
columnNameToFieldName "foo_25bar"  -- Uses Text.Inflections
  -- Result varies, but converting back produces "foo25_bar" ❌

-- After: correct round-trip  
columnNameToFieldName "foo_25bar"  -- "foo25bar"
fieldNameToColumnName "foo25bar"   -- "foo_25bar" ✓

Changes

columnNameToFieldName: Added custom logic when underscore precedes a digit

• Pure digit segments (e.g., "123" from test_123_column) remain as-is; next word segment capitalized
• Mixed digit-letter segments (e.g., "25bar" from foo_25bar) lowercased to encode boundary information

fieldNameToColumnName: Added custom logic for any field name containing digits

• Inserts _ before digits following letters
• Inserts _ before uppercase following lowercase only (not following digits, preserving encoded boundaries)

Test coverage

-- New round-trip tests
foo_25bar      ↔ foo25bar
test_123_column ↔ test123Column  
user_2fa_enabled ↔ user2faEnabled
item_3d_model   ↔ item3dModel

-- Existing behavior preserved
project_id ↔ projectId
user_name  ↔ userName

Original prompt

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This section details on the original issue you should resolve

<issue_title>round-trip error in underscore/titlecasing column names with number after underscore</issue_title>
<issue_description>
https://github.com/unhammer/ihp-back-button-repro/tree/noRoundtripTitleScore
does
ALTER TABLE users ADD COLUMN foo_25bar TEXT DEFAULT null;
which gives
EnhancedSqlError {sqlErrorQuery = "UPDATE users SET id = ?, name = ?, foo_25bar = ? WHERE id = ? RETURNING id, name, foo_25bar", sqlErrorQueryParams = [Plain "id",Escape "test",Plain "foo25_bar",Plain "'97cb49d9-2015-4121-bf55-885ef19dc4f0'"], sqlError = SqlError {sqlState = "42703", sqlExecStatus = FatalError, sqlErrorMsg = "column \"foo25_bar\" does not exist", sqlErrorDetail = "", sqlErrorHint = "Perhaps you meant to reference the column \"users.foo_25bar\"."}}
when trying to save an edit from e.g.
http://localhost:8002/EditUser?userId=97cb49d9-2015-4121-bf55-885ef19dc4f0

Yes I know it's a strange column name :-) but it would be nice if it either 1. worked or 2. was a compilation error.

possibly related:
#1497</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes round-trip error in underscore/titlecasing column names with number after underscore #2073

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