feat(text_embed): Add vLLM as a provider

[desmondcheongzx]

Changes Made

Adds vLLM as a provider for text embedding.

import daft
from daft.ai.provider import load_provider
from daft.functions.ai import embed_text

provider = load_provider("vllm")
model = "Qwen/Qwen3-Embedding-0.6B"

(
    daft.read_huggingface("Open-Orca/OpenOrca")
    .with_column("embedding", embed_text(daft.col("response"), provider=provider, model=model))
    .show()
)

[codecov[bot]]

Codecov Report

:x: Patch coverage is 87.71930% with 7 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 71.92%. Comparing base (81c2e1a) to head (1567b08). :warning: Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
daft/ai/provider.py	16.66%	5 Missing :warning:
daft/ai/vllm/protocols/text_embedder.py	97.22%	1 Missing :warning:
daft/ai/vllm/provider.py	93.33%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5136      +/-   ##
==========================================
- Coverage   76.54%   71.92%   -4.63%     
==========================================
  Files         953      955       +2     
  Lines      130653   130581      -72     
==========================================
- Hits       100006    93918    -6088     
- Misses      30647    36663    +6016     

Files with missing lines	Coverage Δ
daft/ai/vllm/protocols/text_embedder.py	97.22% <97.22%> (ø)
daft/ai/vllm/provider.py	93.33% <93.33%> (ø)
daft/ai/provider.py	47.16% <16.66%> (-8.39%)	:arrow_down:

... and 155 files with indirect coverage changes

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