Add tiktoken as a dependency in pyproject.toml #3403

Job	Run time
format	48s
codecov (./packages/autogen-core)	1m 10s
lint	1m 27s
codecov (./packages/autogen-magentic-one)	1m 57s
codecov (./packages/autogen-ext)	2m 51s
mypy (./packages/autogen-core)	2m 5s
pyright (./packages/autogen-core)	54s
codecov (./packages/autogen-agentchat)	1m 3s
test (./packages/autogen-core)	1m 2s
mypy (./packages/autogen-magentic-one)	1m 45s
pyright (./packages/autogen-magentic-one)	57s
test (./packages/autogen-magentic-one)	1m 29s
mypy (./packages/agbench)	56s
pyright (./packages/agbench)	1m 2s
test (./packages/autogen-ext)	3m 2s
mypy (./packages/autogen-ext)	2m 24s
pyright (./packages/autogen-ext)	1m 12s
test (./packages/autogen-agentchat)	55s
mypy (./packages/autogen-agentchat)	1m 12s
pyright (./packages/autogen-agentchat)	58s
mypy (./packages/magentic-one-cli)	1m 18s
pyright (./packages/magentic-one-cli)	52s
check-proto-changes-python	1m 6s
docs (./packages/autogen-core)	1m 24s
docs-example-check (./packages/autogen-core)	2m 37s
markdown-code-lint	2m 9s
samples-code-check	1m 5s
	39m 40s

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