Update Phupha integration to filter in spell checker

- Changed to use full Phupha dataset (62,264 words) in corpus file
- Added filtering logic in pythainlp/spell/pn.py to filter by thai_orst_words
- This allows the full Phupha dataset to be available for other uses
- Updated tests to verify filtering works correctly
- Spell checker now filters 38,160 ORST words from full Phupha dataset

Co-authored-by: wannaphong <8536487+wannaphong@users.noreply.github.com>

Author: Copilot

pythainlp/corpus/phupha.py

@@ -4,8 +4,6 @@
 """Phupha: Thai Word Frequency Dataset
 
 Phupha is A Thai Word Frequency Dataset from Common Crawl Corpus.
-The dataset is filtered to include only words from the Royal Society of
-Thailand (ORST) word list.
 
 Dataset:
     Phatthiyaphaibun, W. (2026). Phupha: Thai Word Frequency Dataset
@@ -30,11 +28,9 @@
 
 
 def word_freqs() -> list[tuple[str, int]]:
-    """Get word frequency from Phupha dataset (filtered with thai_orst_words)
+    """Get word frequency from Phupha dataset
 
-    Phupha is A Thai Word Frequency Dataset from Common Crawl Corpus,
-    filtered to include only words from the Royal Society of Thailand
-    (ORST) word list.
+    Phupha is A Thai Word Frequency Dataset from Common Crawl Corpus.
 
     :return: List of tuples (word, frequency)
     :rtype: list[tuple[str, int]]
@@ -63,11 +59,9 @@ def word_freqs() -> list[tuple[str, int]]:
 
 
 def unigram_word_freqs() -> dict[str, int]:
-    """Get unigram word frequency from Phupha dataset (filtered with thai_orst_words)
+    """Get unigram word frequency from Phupha dataset
 
-    Phupha is A Thai Word Frequency Dataset from Common Crawl Corpus,
-    filtered to include only words from the Royal Society of Thailand
-    (ORST) word list.
+    Phupha is A Thai Word Frequency Dataset from Common Crawl Corpus.
 
     :return: Dictionary mapping words to their frequencies
     :rtype: dict[str, int]