Add Nepali language support (ne, en_NE) with Devanagari script and test coverage

[sparshrestha]

This pull request adds new language support for both the Nepali numbering system (in Devanagari script) and the English (Nepal) words.

Changes proposed in this pull request:

• lang_NE.py - Native Nepali (ne) with Devanagari script output

  • Cardinal numbers (0-99 direct lookup, larger numbers via composition)
  • Ordinal numbers with Nepali suffixes (पहिलो, दोस्रो, तेस्रो, etc.)
  • Nepali numbering system: लाख (10^5), करोड (10^7), अर्ब (10^9), खर्ब (10^11)
  • Currency support: NPR (रुपैयाँ/पैसा), USD, EUR
  • Negative numbers with माइनस prefix

• lang_EN_NE.py - English (Nepal) variant (en_NE)

  • English words with Nepali/South Asian numbering system
  • Extends additional scale: shankha (10^17), padam (10^15), neel (10^13)

Testing:

• tests/test_ne.py - Devanagari tests

  • Direct cardinal lookup (1-99) with proper Nepali numerals
  • Scale words: हजार, लाख, करोड, अर्ब, खर्ब
  • Complex multi-scale numbers (999,999,999,999)
  • Ordinal conversions, currency conversions with fractional parts
  • Negative numbers, string inputs, float truncation
  • 99999 - उनान्सय हजार नौ सय उनान्सय

• tests/test_en_ne.py - English (Nepal) variant tests

  • Powers of 10 from lakh (10^5) to shankha (10^17)
  • 12345678 - one crore, twenty-three lakh, forty-five thousand, six hundred and seventy-eight

Nepali (ne) Features:

• Full Devanagari numeral vocabulary (शून्य to उनान्सय for 0-99)
• Proper compound word formation without hyphens (एक सय, दुई लाख)
• Currency precision handling with is_int_with_cents=False

English Nepal (en_NE) Features:

• Inherits from Num2Word_EN base with modified scale dictionary
• Maintains English cardinal/ordinal rules with Nepali grouping

Status

• READY
• HOLD
• WIP (Work-In-Progress)

How to verify this change

Run tests locally:

# Test Nepali (Devanagari)
python -m pytest tests/test_ne.py -v

# Test English (Nepal)
python -m pytest tests/test_en_ne.py -v

# Verify code formatting
tox -e isort

Additional notes

If applicable, explain the rationale behind your change.

The dual implementation (ne for native Devanagari, en_NE for English with Nepali numbering) addresses both official documentation needs and business communication contexts where English text follows Nepali's lakh/crore conventions. This closes a critical gap in South Asian language support, enabling proper localization of accounting software (eg: Frappe ERPNext), banking applications, and government e-governance systems serving Nepal's market.

Integration with Frappe Framework:

The Frappe Framework already implements Nepali number system formatting for display purposes (see frappe/public/js/frappe/utils/number_systems.js) with abbreviations like Kh (Kharba), Ar (Arba), Cr (Crore), and L (Lakh).

However, the critical in_words() function in frappe/utils/data.py cannot convert Nepali numbers to words because num2words lacks ne or en_NE locale support.

This PR directly addresses it. Once merged, ERPNext and Frappe-based applications can properly generate invoices, purchase orders, and payment vouchers with Nepali word representations. The implementation follows Frappe's existing pattern where get_number_system('Nepal') returns the Nepali system, but extends it to actual word conversion rather than just display formatting.

Also, extends to #548
References:
Nepali numbers (नेपाली गणना)
Numbers in Nepali language - Wikipedia

[sparshrestha]

@savoirfairelinux @mrodriguezg1991
Please review this PR.

[coveralls]

coverage: 98.088% (-0.1%) from 98.189%
when pulling 03eed40 on sparshrestha:feat/add-nepali-language-support
into 07814cb on savoirfairelinux:master.