fix: withConverter

[imsamgarg]

now support firestore documents with custom converter

before documents initiated with withConverter collection couldn't be passed into function because
function takes DocumentReference<Map<String,dynamic>> type but our doc is DocumentReference type

error befor---
`
final doc=i.collection("col").withConverter(fromFirestore: fromFirestore, toFirestore: toFirestore).doc("doc");

`

[codecov]

Codecov Report

Merging #99 (4404ff1) into main (e13e3a8) will decrease coverage by 13.15%.
The diff coverage is 64.28%.

@@             Coverage Diff              @@
##              main      #99       +/-   ##
============================================
- Coverage   100.00%   86.84%   -13.16%     
============================================
  Files            1        1               
  Lines           31       38        +7     
============================================
+ Hits            31       33        +2     
- Misses           0        5        +5     

Impacted Files	Coverage Δ
lib/src/firestore_cache.dart	86.84% <64.28%> (-13.16%)	⬇️

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[zeshuaro]

Thanks for raising this PR. Would you be able to address these comments?

[zeshuaro]

I can understand the use case for Query<T> then returning QuerySnapshot<T>. But can people simply pass in the default Map<String, dynamic> for cacheDocRef? For the example code you shared, can you pass in FirebaseFirestore.instance.doc('col/doc') instead? This document is simply used for fetching the cache date info, so I would imagine there's no need to use the parameter with the converters.

Also, I don't think it can use the same type T which is used for Query and the returned QuerySnapshot>, as it probably has a different type.