chore: Make PyStemmer optional

[generall]

No description provided.

[joein]

Pystemmer is a C library wrapper which enhances the speed of the tokenizer

I ran the following benchmark with and without it:

import time
from snowballstemmer import stemmer

s = stemmer('english')
text = "This stem form is often a word itself, but this is not always the case as this is not a requirement for text search systems, which are the intended field of use. We also aim to conflate words with the same meaning, rather than all words with a common linguistic root (so awe and awful don't have the same stem), and over-stemming is more problematic than under-stemming so we tend not to stem in cases that are hard to resolve. If you want to always reduce words to a root form and/or get a root form which is itself a word then Snowball's stemming algorithms likely aren't the right answer."
words = text.split()

loops = 1000
a = time.perf_counter()
for _ in range(loops):
    for word in words:
        stemmed = s.stemWord(word)
print(time.perf_counter() - a)

With pystemmer:
0.0221869999950286
Without pystemmer:
2.5555163340177387

The difference is noticeable, instead of dropping it, we can make it an optional dependency and allow to install it with pip install fastembed[pystemmer]
According to the users' reports, it crashes on windows during the installation, and not on the level of dependency resolution

[Anush008]

@joein. Review please. Several people are running into this issue.

[bendominguez0111]

Hello, any update on this? Our team is running into issues with PyStemmer and we'd like the option for it to be optional as well.

[satyaloka93]

Also would like to make this dependency optional,having issues with the building of PyStemmer.

[sadaisystems]

Same issue here. WSL2. Python 3.12.5. Unable to install the package.

[satyaloka93]

I've been installing version 0.2.7, which basically has the same dependencies as the newest version minus pystemmer. Then I install the new version with --no-deps, to avoid that package. It's been working fine, please remove that one requirement and make it an option!

[Anush008]

Resolved with https://github.com/qdrant/fastembed/releases/tag/v0.4.1