Replace HasUID with IsChunk in drasil-lang type constraints

[Copilot]

Migrates all HasUID constraints in drasil-lang to IsChunk, strengthening the type system to require proper chunk dependency tracking via HasChunkRefs.

Background

IsChunk is a constraint alias combining three requirements:

type IsChunk a = (HasUID a, HasChunkRefs a, Typeable a)

Previously, many type signatures only required HasUID, allowing chunks without dependency tracking.

Changes

Added Missing HasChunkRefs Instances (9 types)

Types with HasUID but missing HasChunkRefs:

• Code generation: CodeChunk, CodeVarChunk, CodeFuncChunk
• Document structure: Section, DecRef
• Chunk types: RelationConcept, UnitalChunk, CI, ConstrConcept, UncertQ, QDefinition

All instances use stub implementation per instructions:

instance HasChunkRefs X where
  chunkRefs = const mempty -- FIXME: `chunkRefs` should actually collect the referenced chunks.

Replaced Constraints in Type Signatures

Class constraints:

• NamedIdea: class HasUID c => NamedIdea c → class IsChunk c => NamedIdea c
• Referable: class (HasUID s, ...) => Referable s → class (IsChunk s, ...) => Referable s

Function constraints (24 functions across 7 modules):

-- Before
apply :: (HasUID f, HasSymbol f) => f -> [r] -> r
sy :: (HasUID c, HasSymbol c) => c -> r

-- After  
apply :: (IsChunk f, HasSymbol f) => f -> [r] -> r
sy :: (IsChunk c, HasSymbol c) => c -> r

Affected modules:

• Drasil.Code.CodeExpr.Class (6 functions)
• Language.Drasil.Expr.Class (5 functions)
• Language.Drasil.Reference (5 functions)
• Language.Drasil.ModelExpr.Class (2 functions)
• Language.Drasil.DecoratedReference (2 functions)
• Language.Drasil.Chunk.Eq (3 functions)
• Language.Drasil.Sentence (1 function)

Impact

16 files modified. All changes are backwards compatible at the call site level—existing code satisfying HasUID constraints will continue to work if types also implement HasChunkRefs (which they now do).

Original prompt

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This section details on the original issue you should resolve

<issue_title>Switch all HasUID usage in drasil-lang to IsChunk.</issue_title>
<issue_description>We should switch all HasUID usage in drasil-lang to IsChunk.

Originally posted by @balacij in #4716 (comment)
</issue_description>

<agent_instructions>All HasUID usage in drasil-lang and related packages really should be IsChunk. Go through all of them and replace them with IsChunk.

For any type (X) that does not satisfy IsChunk's HasChunkRefs constraint, you should instantiate it using the following TEMPLATE code underneath the definition of said type:

instance HasChunkRefs X where
  chunkRefs = const mempty -- FIXME: `chunkRefs` should actually collect the referenced chunks.

Do not try to fill in chunkRefs properly. Restrict yourself to only replacing X from the template, adding it in places as necessary.</agent_instructions>

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

• Fixes Switch all HasUID usage in drasil-lang to IsChunk. #4717

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[balacij]

Closing this in favour of restarting on my own using: #4723 and #4724 as a base.