exa docs and python package update (#31307)

Added support for new Exa API features. Updated Exa docs and python
package (langchain-exa).

Description

Added support for new Exa API features in the langchain-exa package:
- Added max_characters option for text content
- Added support for summary and custom summary prompts
- Added livecrawl option with "always", "fallback", "never" settings
- Added "auto" option for search type
- Updated documentation and tests

Dependencies
- No new dependencies required. Using existing features from exa-py.

twitter: @theishangoswami

---------

Co-authored-by: Chester Curme <chester.curme@gmail.com>

libs/partners/exa/README.md

@@ -27,6 +27,30 @@ results  = exa.invoke("What is the capital of France?")
 print(results)
 ```
 
+### Advanced Features
+
+You can use advanced features like text limits, summaries, and live crawling:
+
+```python
+from langchain_exa import ExaSearchRetriever, TextContentsOptions
+
+# Create a new instance with advanced options
+exa = ExaSearchRetriever(
+    exa_api_key="YOUR API KEY",
+    k=20,  # Number of results (1-100)
+    type="auto",  # Can be "neural", "keyword", or "auto"
+    livecrawl="always",  # Can be "always", "fallback", or "never"
+    summary=True,  # Get an AI-generated summary of each result
+    text_contents_options={"max_characters": 3000}  # Limit text length
+)
+
+# Search for a query with custom summary prompt
+exa_with_custom_summary = ExaSearchRetriever(
+    exa_api_key="YOUR API KEY",
+    summary={"query": "generate one line summary in simple words."}  # Custom summary prompt
+)
+```
+
 ## Exa Search Results
 
 You can run the ExaSearchResults module as follows
@@ -48,6 +72,33 @@ search_results = search_tool._run(
 print("Search Results:", search_results)
 ```
 
+### Advanced Features
+
+You can use advanced features like text limits, summaries, and live crawling:
+
+```python
+from langchain_exa import ExaSearchResults
+
+# Initialize the ExaSearchResults tool
+search_tool = ExaSearchResults(exa_api_key="YOUR API KEY")
+
+# Perform a search query with advanced options
+search_results = search_tool._run(
+    query="Latest AI research papers",
+    num_results=10,  # Number of results (1-100)
+    type="auto",  # Can be "neural", "keyword", or "auto"
+    livecrawl="always",  # Can be "always", "fallback", or "never"
+    summary=True,  # Get an AI-generated summary of each result
+    text_contents_options={"max_characters": 2000}  # Limit text length
+)
+
+# With custom summary prompt
+search_results_with_custom_summary = search_tool._run(
+    query="Latest AI research papers",
+    summary={"query": "generate one liner"}  # Custom summary prompt
+)
+```
+
 ## Exa Find Similar Results
 
 You can run the ExaFindSimilarResults module as follows
@@ -67,4 +118,22 @@ similar_results = find_similar_tool._run(
 )
 
 print("Similar Results:", similar_results)
+```
+
+### Advanced Features
+
+```python
+from langchain_exa import ExaFindSimilarResults
+
+# Initialize the ExaFindSimilarResults tool
+find_similar_tool = ExaFindSimilarResults(exa_api_key="YOUR API KEY")
+
+# Find similar results with advanced options
+similar_results = find_similar_tool._run(
+    url="http://espn.com",
+    num_results=10,  # Number of results (1-100)
+    livecrawl="fallback",  # Can be "always", "fallback", or "never"
+    summary=True,  # Get an AI-generated summary of each result
+    text_contents_options={"max_characters": 1500}  # Limit text length
+)
 ```