uv add should preserve alphabetic package ordering

[konstin]

Currently, uv add always adds new entries last. It should instead preserve a lexicographic order if one is used.

Example: Running uv add "pydantic >=2.7.1" on:

[project]
dependencies = [
    "CacheControl[filecache]>=0.14,<0.15",
    "mwparserfromhell >=0.6.4,<0.7",
    "pywikibot >=9.1.2,<10",
    "sentry-sdk >=2.0.1,<3",
    "yarl >=1.9,<2",
    "pydantic>=2.7.1",
]

Current output:

[project]
dependencies = [
    "CacheControl[filecache]>=0.14,<0.15",
    "mwparserfromhell >=0.6.4,<0.7",
    "pywikibot >=9.1.2,<10",
    "sentry-sdk >=2.0.1,<3",
    "yarl >=1.9,<2",
    "pydantic>=2.7.1",
]

Desired output:

[project]
dependencies = [
    "CacheControl[filecache]>=0.14,<0.15",
    "mwparserfromhell >=0.6.4,<0.7",
    "pydantic >=2.7.1",
    "pywikibot >=9.1.2,<10",
    "sentry-sdk >=2.0.1,<3",
    "yarl >=1.9,<2",
]