DOC: Revise target timelines for roadmap features (#510)

Updated target timelines for several features in the roadmap.

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[AB#43952](https://sqlclientdrivers.visualstudio.com/c6d89619-62de-46a0-8b46-70b92a84d85e/_workitems/edit/43952)

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This pull request updates the feature roadmap in `ROADMAP.md` to adjust
the planned timelines for several upcoming features. The main changes
are revised target dates for features such as returning rows as
dictionaries, asynchronous query execution, vector datatype support,
table-valued parameters, and JSON datatype support.

Roadmap timeline updates:

* Changed the target timeline for "Return Rows as Dictionaries" to Q3
2026.
* Changed the target timeline for "Asynchronous Query Execution" to Q4
2026.
* Changed the target timeline for "Vector Datatype Support" to Q3 2026.
* Changed the target timeline for "Table-Valued Parameters (TVPs)" to Q3
2026.
* Changed the target timeline for "JSON Datatype Support" to Q4 2026.
-------------------------------------------------------------------
### Summary   
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required. -->
This pull request updates the feature roadmap in `ROADMAP.md` to revise
the target timelines for several planned features. The most important
changes are:

Roadmap timeline updates:

* Changed the target timeline for "Return Rows as Dictionaries" from Q4
2025 to Q3 2026.
* Changed the target timeline for "Asynchronous Query Execution" from Q1
2026 to Q4 2026.
* Changed the target timeline for "Vector Datatype Support" from Q1 2026
to Q3 2026.
* Changed the target timeline for "Table-Valued Parameters (TVPs)" from
Q1 2026 to Q3 2026.
* Changed the target timeline for "JSON Datatype Support" from "ETA will
be updated soon" to Q4 2026.

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Author: sumitmsft

ROADMAP.md

@@ -4,15 +4,8 @@ The following roadmap summarizes the features planned for the Python Driver for
 
 | Feature                        | Description                                                       | Status       | Target Timeline          |
 | ------------------------------ | ----------------------------------------------------------------- | ------------ | ------------------------ |
-| Parameter Dictionaries         | Allow parameters to be supplied as Python dicts                   | Planned      | Q4 2025                  |
-| Return Rows as Dictionaries    | Fetch rows as dictionaries for more Pythonic access               | Planned      | Q4 2025                  |
-| Bulk Copy (BCP)                | High-throughput ingestion API for ETL workloads                   | Under Design | Q1 2026                  |
-| Asynchronous Query Execution   | Non-blocking queries with asyncio support                         | Planned      | Q1 2026                  |
-| Vector Datatype Support        | Native support for SQL Server vector datatype                     | Planned      | Q1 2026                  |
-| Table-Valued Parameters (TVPs) | Pass tabular data structures into stored procedures               | Planned      | Q1 2026                  |
-| C++ Abstraction                | Modular separation via pybind11 for performance & maintainability | In Progress  | ETA will be updated soon |
-| JSON Datatype Support          | Automatic mapping of JSON datatype to Python dicts/lists          | Planned      | ETA will be updated soon |
-| callproc()                     | Full DBAPI compliance & stored procedure enhancements             | Planned      | ETA will be updated soon |
-| setinputsize()                 | Full DBAPI compliance & stored procedure enhancements             | Planned      | ETA will be updated soon |
-| setoutputsize()                | Full DBAPI compliance & stored procedure enhancements             | Planned      | ETA will be updated soon |
-| Output/InputOutput Params      | Full DBAPI compliance & stored procedure enhancements             | Planned      | ETA will be updated soon |
+| Return Rows as Dictionaries    | Fetch rows as dictionaries for more Pythonic access               | Planned      | Q3 2026                  |
+| Asynchronous Query Execution   | Non-blocking queries with asyncio support                         | Planned      | Q4 2026                  |
+| Vector Datatype Support        | Native support for SQL Server vector datatype                     | Planned      | Q3 2026                  |
+| Table-Valued Parameters (TVPs) | Pass tabular data structures into stored procedures               | Planned      | Q3 2026                  |
+| JSON Datatype Support          | Automatic mapping of JSON datatype to Python dicts/lists          | Planned      | Q4 2026                  |