Merge dplyr-style chainable API into DSL v2 builder

[Copilot]

The library had two separate APIs for chainable operations: graph_ops.py (dplyr-style) and dsl/builder.py (query builder), forcing users to learn and switch between both. This consolidates them into a unified interface.

Changes

DSL Builder (py3plex/dsl/builder.py)

• Added 11 dplyr-style methods to QueryBuilder: filter(), filter_expr(), head(), tail(), take(), sample(), slice(), first(), last(), pluck(), collect()
• filter() aliases existing where() for traditional dplyr naming
• filter_expr() enables string-based filtering with safe AST evaluation
• Sampling and slicing methods provide pandas-like data manipulation

Executor (py3plex/dsl/executor.py)

• Extended _apply_post_filters() to handle new filter types (expression, tail, sample, slice, last)
• Added _safe_eval_expr() for secure expression evaluation using AST validation
• Filters applied pre-compute for efficiency where possible

Documentation

• Updated AGENTS.md to document unified API
• Enhanced example_dsl_dplyr_operations.py with demonstration of new methods
• Added comprehensive test suite (tests/test_dplyr_integration.py)

Example

from py3plex.dsl import Q, L

# Before: separate APIs
from py3plex.graph_ops import nodes
df = nodes(net).filter(lambda n: n["degree"] > 5).to_pandas()

# After: unified builder API
df = (
    Q.nodes()
     .compute("degree")
     .filter(degree__gt=5)           # dplyr-style filter
     .filter_expr("layer == 'ppi'")  # string-based filtering  
     .arrange("-degree")
     .head(10)
     .sample(5, seed=42)
     .execute(net)
     .to_pandas()
)

Backward Compatibility: Standalone graph_ops module remains available. No breaking changes to existing DSL v2 functionality.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>dplyr in dsl2</issue_title>
<issue_description>merge dplyr style chainable api into dslV2 (builder), to reduce cognitive load and simplify. no new md allowed, make sure tests pass//functionality is preserved. Update all docs/examples where relevant</issue_description>

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

• Fixes dplyr in dsl2 #997

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.